Update client-server API endpoints to move from r0 to v3 (plus whitespace fixes) (#3421)

* Blind find & replace all on client major version -> v3

* Fix up bad replacements

* Fix anchors for r0->v3

* Changelog

data/api/client-server/joining.yaml

@@ -19,7 +19,7 @@ host: localhost:8008
 schemes:
   - https
   - http
-basePath: /_matrix/client/%CLIENT_MAJOR_VERSION%
+basePath: /_matrix/client/v3
 consumes:
   - application/json
 produces:
@@ -40,8 +40,8 @@ paths:
         events associated with the room until the user leaves the room.
 
         After a user has joined a room, the room will appear as an entry in the
-        response of the [`/initialSync`](/client-server-api/#get_matrixclientr0initialsync)
-        and [`/sync`](/client-server-api/#get_matrixclientr0sync) APIs.
+        response of the [`/initialSync`](/client-server-api/#get_matrixclientv3initialsync)
+        and [`/sync`](/client-server-api/#get_matrixclientv3sync) APIs.
       operationId: joinRoomById
       security:
         - accessToken: []
@@ -117,8 +117,8 @@ paths:
         events associated with the room until the user leaves the room.
 
         After a user has joined a room, the room will appear as an entry in the
-        response of the [`/initialSync`](/client-server-api/#get_matrixclientr0initialsync)
-        and [`/sync`](/client-server-api/#get_matrixclientr0sync) APIs.
+        response of the [`/initialSync`](/client-server-api/#get_matrixclientv3initialsync)
+        and [`/sync`](/client-server-api/#get_matrixclientv3sync) APIs.
       operationId: joinRoom
       security:
         - accessToken: []