See which Mutual Rooms you share with a user

[ShadowJonathan]

Describe the problem

I would like to see which rooms I share with a user, which could be useful before accepting a DM from them, or to cross-reference where i have seen someone before.

Describe the solution you'd like

MSC2666, which is implemented in js-sdk as https://github.com/matrix-org/matrix-js-sdk/pull/1417 (with a name-change in https://github.com/matrix-org/matrix-js-sdk/pull/2271)

Integrating this in Cinny would help identify common rooms you'd have with another user.

Alternatives considered

No response

Additional context

No response