Implement Third Party Lookups

[matrixbot]

This issue was originally created by @babolivier at matrix-org/dendrite#633.

• Implement GET /_matrix/client/r0/thirdparty/protocols
• Implement GET /_matrix/client/r0/thirdparty/protocol/{protocol}
• Implement GET /_matrix/client/r0/thirdparty/location/{protocol}
• Implement GET /_matrix/client/r0/thirdparty/user/{protocol}
• Implement GET /_matrix/client/r0/thirdparty/location
• Implement GET /_matrix/client/r0/thirdparty/user

[matrixbot]

This comment was originally posted by @babolivier at matrix-org/dendrite#633 (comment).

Actually there's a PR open for this: matrix-org/dendrite#561

[matrixbot]

This comment was originally posted by @kegsay at matrix-org/dendrite#633 (comment).

Sytests:

    × Can invite existing 3pid
    × Can invite existing 3pid with no ops into a private room
    × Can invite existing 3pid in createRoom
    × Can invite unbound 3pid
    × Can invite unbound 3pid over federation
    × Can invite unbound 3pid with no ops into a private room
    × Can invite unbound 3pid over federation with no ops into a private room
    × Can invite unbound 3pid over federation with users from both servers
    × Can accept unbound 3pid invite after inviter leaves
    × Can accept third party invite with /join
    × Can bind 3PID via home server
    × Can bind and unbind 3PID via homeserver
    × Can unbind 3PID via homeserver when bound out of band
    × 3PIDs are unbound after account deactivation
    × Can bind and unbind 3PID via /unbind by specifying the identity server
    × Can bind and unbind 3PID via /unbind without specifying the identity server

[matrixbot]

This comment was originally posted by @jittygitty at matrix-org/dendrite#633 (comment).

@spaetz Was that PR matrix-org/dendrite#561 to address this deserted for any particular technical reason? I know its not "needed" to fix that Element Desktop app issue but was still wondering about #561