Move raw API and event schemas into /data directory

Historical note: this was originally a series of several commits, spread out
over several weeks. They have been squashed together to make `git annotate`
work properly.

The original commits were:
 * 91ab3934 <Will> 2021-01-25 21:16:42 -0800 Add raw API end event schemas into /data directory
 * aae22f47 <Will> 2021-01-25 21:33:06 -0800 Remove non-data files
 * 1092d4ca <Will> 2021-01-26 20:41:33 -0800 Add data-compatiuble extension (.yaml) to all data files that currently omit one
 * 21060109 <Will> 2021-01-26 20:57:28 -0800 Remove symlink to event-schemas, and update openAPI schema paths accordingly
 * 4f633845 <Travis Ralston> 2021-04-12 21:54:54 -0600 Fix event schema examples too
 * 301c7b2f <Will> 2021-02-05 10:15:42 -0800 Restore docs describing OpenAPI extensions that we use

data/event-schemas/schema/core-event-schema/event.yaml

@@ -0,0 +1,15 @@
+description: The basic set of fields all events must have.
+properties:
+  content:
+    description: The fields in this object will vary depending on the type of event.
+      When interacting with the REST API, this is the HTTP body.
+    type: object
+  type:
+    description: The type of event. This SHOULD be namespaced similar to Java package
+      naming conventions e.g. 'com.example.subdomain.event.type'
+    type: string
+required:
+  - type
+  - content
+title: Event
+type: object

data/event-schemas/schema/core-event-schema/msgtype_infos/image_info.yaml

@@ -0,0 +1,36 @@
+$schema: http://json-schema.org/draft-04/schema#
+description: Metadata about an image.
+properties:
+  h:
+    description: |-
+      The intended display height of the image in pixels. This may
+      differ from the intrinsic dimensions of the image file.
+    type: integer
+  w:
+    description: |-
+      The intended display width of the image in pixels. This may
+      differ from the intrinsic dimensions of the image file.
+    type: integer
+  mimetype:
+    description: The mimetype of the image, e.g. ``image/jpeg``.
+    type: string
+  size:
+    description: Size of the image in bytes.
+    type: integer
+  thumbnail_url:
+    description: |-
+      The URL (typically `MXC URI`_) to a thumbnail of the image.
+      Only present if the thumbnail is unencrypted.
+    type: string
+  thumbnail_file:
+    description: |-
+      Information on the encrypted thumbnail file, as specified in
+      |encrypted_files|_. Only present if the thumbnail is encrypted.
+    title: EncryptedFile
+    type: object
+  thumbnail_info:
+    allOf:
+      - $ref: thumbnail_info.yaml
+    description: Metadata about the image referred to in ``thumbnail_url``.
+title: ImageInfo
+type: object

data/event-schemas/schema/core-event-schema/msgtype_infos/thumbnail_info.yaml

@@ -0,0 +1,21 @@
+$schema: http://json-schema.org/draft-04/schema#
+description: Metadata about a thumbnail image.
+properties:
+  h:
+    description: |-
+      The intended display height of the image in pixels. This may
+      differ from the intrinsic dimensions of the image file.
+    type: integer
+  w:
+    description: |-
+      The intended display width of the image in pixels. This may
+      differ from the intrinsic dimensions of the image file.
+    type: integer
+  mimetype:
+    description: The mimetype of the image, e.g. ``image/jpeg``.
+    type: string
+  size:
+    description: Size of the image in bytes.
+    type: integer
+title: ThumbnailInfo
+type: object

data/event-schemas/schema/core-event-schema/room_event.yaml

@@ -0,0 +1,13 @@
+allOf:
+- $ref: sync_room_event.yaml
+description: Room Events have the following fields.
+properties:
+  room_id:
+    description: |-
+      The ID of the room associated with this event. Will not be present on events
+      that arrive through ``/sync``, despite being required everywhere else.
+    type: string
+required:
+- room_id
+title: RoomEvent
+type: object

data/event-schemas/schema/core-event-schema/state_event.yaml

@@ -0,0 +1,6 @@
+allOf:
+- $ref: room_event.yaml
+- $ref: sync_state_event.yaml
+description: State Events have the following fields.
+title: StateEvent
+type: object

data/event-schemas/schema/core-event-schema/sync_room_event.yaml

@@ -0,0 +1,43 @@
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Note: this is technically not a core event schema, however it is included here
+# to keep things sane. The short story is that /sync doesn't require a room_id to
+# be on events, so we give it a whole event structure as a base for room_event.
+# This base doesn't declare a room_id, which instead appears in the room_event.
+
+allOf:
+- $ref: event.yaml
+description: In addition to the Event fields, Room Events have the following additional
+  fields.
+properties:
+  event_id:
+    description: The globally unique event identifier.
+    type: string
+  sender:
+    description: Contains the fully-qualified ID of the user who sent this event.
+    type: string
+  origin_server_ts:
+    description: Timestamp in milliseconds on originating homeserver
+      when this event was sent.
+    type: integer
+    format: int64
+  unsigned:
+    $ref: unsigned_prop.yaml
+required:
+- event_id
+- sender
+- origin_server_ts
+title: SyncRoomEvent
+type: object

data/event-schemas/schema/core-event-schema/sync_state_event.yaml

@@ -0,0 +1,39 @@
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# See sync_room_event.yaml for why this file is here.
+
+allOf:
+- $ref: sync_room_event.yaml
+description: In addition to the Room Event fields, State Events have the following
+  additional fields.
+properties:
+  prev_content:
+    description: Optional. The previous ``content`` for this event. If there is no
+      previous content, this key will be missing.
+    title: EventContent
+    type: object
+  state_key:
+    description: A unique key which defines the overwriting semantics for this piece
+      of room state. This value is often a zero-length string. The presence of this
+      key makes this event a State Event.
+
+      State keys starting with an ``@`` are reserved for referencing user IDs, such
+      as room members. With the exception of a few events, state events set with a
+      given user's ID as the state key MUST only be set by that user.
+    type: string
+required:
+- state_key
+title: SyncStateEvent
+type: object

data/event-schemas/schema/core-event-schema/unsigned_prop.yaml

@@ -0,0 +1,34 @@
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+title: UnsignedData
+type: object
+description: Contains optional extra information about the event.
+properties:
+  age:
+    description: The time in milliseconds that has elapsed since the event was
+      sent. This field is generated by the local homeserver, and may be incorrect
+      if the local time on at least one of the two servers is out of sync, which can
+      cause the age to either be negative or greater than it actually is.
+    type: integer
+  redacted_because:
+    description: The event that redacted this event, if any.
+    title: Event
+    type: object
+  transaction_id:
+    description: |
+      The client-supplied transaction ID, for example, provided via
+      ``PUT /_matrix/client/r0/rooms/{roomId}/send/{eventType}/{txnId}``,
+      if the client being given the event is the same one which sent it.
+    type: string