Implement MSC2346 (bridge info state event) for PMs

[progval]

This PR depends on the following:

• https://github.com/matrix-org/matrix-appservice-bridge/pull/460 for typing
• https://github.com/matrix-org/matrix-appservice-irc/pull/1681 to allow tests to turn MSC2346 on

[progval]

Signed-off-by: Valentin Lorentz \<progval plus matrixsignoff at progval dot net>

[progval]

ping?

[progval]

ping?