Element R: Persistent room list

[richvdh]

Legacy crypto has a RoomList which maintains a list of encrypted rooms inside the CryptoStore. We probably need to do something with this (otherwise the server could trick us into resetting the encryption settings of a room).

• Add support to matrix-sdk-crypto for getting and setting room settings (crypto: Implement OlmMachine::{set_,}room_settings matrix-org/matrix-rust-sdk#3042)
• [c] Expose those methods in wasm bindings (Support for saving and loading room settings matrix-org/matrix-rust-sdk-crypto-wasm#95)
• Get rid of MatrixClient.roomList, and let legacy Crypto instantiate its own. Replace the two references to it inside MatrixClient with a CryptoBackend.isRoomEncrypted or similar. (Done in Move roomList out of MatrixClient, into legacy Crypto matrix-org/matrix-js-sdk#3944)
• Implement for RustCrypto via bindings added above
• In RustCrypto.onCryptoEvent, check existing setting, and store updates.
• In MatrixClient.encryptEventIfNeeded, make sure that the crypto store is checked. (Element-R: check persistent room list for encryption config matrix-org/matrix-js-sdk#4035)

(https://docs.google.com/document/d/18LuSmlaoeZpsOsiPKIdAxKYsbr9V1etMAYm2vxMId7A/edit#heading=h.t75m7z578qe4)

[andybalaam]

The RoomList module is referred to as matrix-js-sdk/src/crypto/RoomList in matrix-react-sdk. The RoomList class is not actually used, but IRoomEncryption from that module is used.

I am wondering whether we should deprecate RoomList (or really deprecate the fact that it is public?) since we want to make it more of an implementation detail of the crypto.