A new widget action called update_state was recently added to MSC2762.

The embedded RoomWidgetClient should use this capability where available in order to get saner room state semantics.

n.b. The was a previous PR to implement this in #4574 but then reverted in #4656 as it was not backwards compatible.

(@robintown says…) However, we don't strictly need backwards compatibility here. The minimum we need is for Element Call (as the primary consumer of the RoomWidgetClient) to be upgraded to a version of matrix-js-sdk compatible with update_state only once we have support for update_state on all widget host that officially support Element Call. That means we need both Element Web and Element X (via matrix-rust-sdk) to support this in their widget drivers, then we can go ahead with this change.