Element-R: Handle incoming verification requests

[richvdh]

Build on outgoing verification (#24983, #25316, #25319).

• Define a new cypress test. Flow should be:

  • Create a “bot” account with bootstrapped cross signing
  • Log into the same account
  • Dismiss the “verify this device” dialog
  • From the bot device, call MatrixClient.requestVerification
  • Go through the verification process.
  • At the end, download the device keys and check that it is cross-signed.

  Estimate: 1d
  Cypress test for incoming verification requests matrix-org/matrix-react-sdk#11123

• Implement in RustCrypto. We need to:

  • Monitor for incoming m.key.verification.request messages
  • Call OlmMachine::get_verification_request and convert to a VerificationRequest as above
  • Tell MatrixClient to emit a CryptoEvent.VerificationRequest.
    • Possibly this means having RustCrypto extend TypedEventEmitter, and making MatrixClient reemit.
  • js-sdk integration test: extend the one added earlier

  Estimate: 1d