Invisible Crypto: Web: display a warning when an *unverified* user changes identity

[richvdh]

Followup to #2492. Part of #2491, itself part of Invisible crypto.

When an unverified user changes their identity, we need to make our user aware of this. In the long term, the intention is just to show a notice in the timeline (#2493); however, that is difficult to implement and we need a stop-gap.

This task is for Element Web.

The proposal is to show a warning above the composer, in much the same way as we would for verified users (#2491), but without locking the composer.

Figma designs:

• Web:
  

[richvdh]

Implementation notes:

• in matrix-sdk-crypto, we need to extend UserIdentities to expose identity_needs_user_approval not sure this is needed
• in matrix-sdk-crypto-wasm, extend UserIdentity and OwnUserIdentity to expose identity_needs_user_approval
  • already done for UserIdentity by Update to latest Rust SDK matrix-org/matrix-rust-sdk-crypto-wasm#141. Don't think it's needed for OwnUserIdentity.
• in matrix-js-sdk, extend RustCrypto.getUserVerificationStatus and UserVerificationStatus to include identityNeedsUserApproval
  • Add CryptoApi.pinCurrentUserIdentity and UserIdentity.needsUserApproval matrix-org/matrix-js-sdk#4415
• in matrix-react-sdk, create a component which will:
  • on start, call Room.getEncryptionTargetMembers to get a list of users of interest, and then call getUserVerificationStatus on each, to build a list of users with pin violations
  • register callback for room membership updates; when we get one, check if the user is on the target encryption list, and check for pin violations (or remove from list if they have left)
  • register callback for trust updates; when we get one:
    • if the user is not in our list and there is a pin violation, check if they are on the target encryption list, and update the list if so
    • if the user is on our list and there is not a pin violation, remove them immediately

[andybalaam]

It would be great if we can re-use the logic I am writing here matrix-org/matrix-rust-sdk@main...andybalaam/room-identity-stream .

The core logic is inside the crypto crate, so there is some chance we can re-use it.