Send device list changes to application services as specified by [MSC3202](https://github.com/matrix-org/matrix-spec-proposals/pull/3202), using unstable prefixes. The `msc3202_transaction_extensions` experimental homeserver config option must be enabled and `org.matrix.msc3202: true` must be present in the application service registration file for device list changes to be sent. The "left" field is currently always empty.
Fix a long-standing bug that updating the server notices user profile (display name/avatar URL) in the configuration would not be applied to pre-existing rooms. Contributed by Jorge Florian.
Switch to using a sequence to generate AS transaction IDs. Contributed by Nick Beeper. If running synapse with a dedicated appservice worker, this MUST be stopped before upgrading the main process and database.
Fix non-member state events not resolving for historical events when used in [MSC2716](https://github.com/matrix-org/matrix-spec-proposals/pull/2716) `/batch_send` `state_events_at_start`.
Fix a long-standing bug affecting URL previews that would generate a 500 response instead of a 403 if the previewed URL includes a port that isn't allowed by the relevant blacklist.