* Stop sharing state observables when the view model is destroyed
By default, observables running with shareReplay will continue running forever even if there are no subscribers. We need to stop them when the view model is destroyed to avoid memory leaks and other unintuitive behavior.
* Hydrate the call view model in a less hacky way
This ensures that only a single view model is created per call, unlike the previous solution which would create extra view models in strict mode which it was unable to dispose of. The other way was invalid because React gives us no way to reliably dispose of a resource created in the render phase. This is essentially a memory leak fix.
* Add simple global controls to put the call in picture-in-picture mode
Our web and mobile apps (will) all support putting calls into a picture-in-picture mode. However, it'd be nice to have a way of doing this that's more explicit than a breakpoint, because PiP views could in theory get fairly large. Specifically, on mobile, we want a way to do this that can tell you whether the call is ongoing, and that works even without the widget API (because we support SPA calls in the Element X apps…)
To this end, I've created a simple global "controls" API on the window. Right now it only has methods for controlling the picture-in-picture state, but in theory we can expand it to also control mute states, which is current possible via the widget API only.
* Fix footer appearing in large PiP views
* Add a method for whether you can enter picture-in-picture mode
* Have the controls emit booleans directly
