Element-R: Emit CryptoEvent.UserTrustStatusChanged when user identity is updated

[richvdh]

Fixes https://github.com/vector-im/crypto-internal/issues/148

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This change is marked as an internal change (Task), so will not be included in the changelog.

[richvdh]

This is currently awaiting a release of rust-sdk-crypto-wasm, but more difficult than that: it introduces a reference cycle in the rust side.

Basically, once I call OlmMachine::user_identities_stream, the cryptostore isn't being dropped when the OlmMachine is dropped.

What seems to be happening is as follows:

• user_identities_stream takes a copy of the VerificationMachine. The new copy holds a ref to the CryptoStoreWrapper.
• The new copy is used in a Stream::map closure ... so is retained until the stream is dropped.
• I have a reader which reads the stream to exhaustion
• The stream reaches exhaustion when the sender end of the BroadcastStream is dropped
• However, the sender is a member of CryptoStoreWrapper, so is never dropped, because of the reference in the Stream::map closure.

So in short, we have a reference cycle which stops the store being cleaned up.

[richvdh]

but more difficult than that: it introduces a reference cycle in the rust side.

This is fixed by matrix-org/matrix-rust-sdk-crypto-wasm#31

[andybalaam]

Looks good, as far as I understand it, which is not a great deal.

[andybalaam]

I suspect the test failure was flakiness, re-adding to merge queue.

For the record, the failure was:

FAIL test/components/views/settings/JoinRuleSettings-test.tsx (7.445 s)
  ● <JoinRuleSettings /> › knock rooms › when room does not support join rule knock › upgrades room when changing join rule to knock

    expect(element).toBeInTheDocument()

    element could not be found in the document

      227 |
      228 |                 // update spaces
    > 229 |                 expect(await screen.findByText("Updating space...")).toBeInTheDocument();
          |                                                                      ^
      230 |
      231 |                 await flushPromises();
      232 |

      at Object.toBeInTheDocument (test/components/views/settings/JoinRuleSettings-test.tsx:229:70)

[andybalaam]

If it merges, we should add a flaky test issue, similar but not identical to element-hq/element-web#25625