Ensure cross-signing keys are downloaded when checking trust
Ensure cross-signing keys are downloaded when checking trust

When checking cross-signing trust during login, we may not have downloaded keys
yet. This ensures we make an attempt first if needed.

Fixes https://github.com/vector-im/riot-web/issues/12068

matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk