Use native video call picture in picture!

[pixlwave]

This PR uses an AVPictureInPictureVideoCallController to PiP the whole EC web view instead of the previous solution where EC would request the web view to PiP the speaker's video. I've made the feature flag user configurable now as it no longer requires a specific EC deployment*.

This PR doesn't handle responses from the web view about whether PiP is possible so it is possible to get stuck in a call when an error occurs.

The second and third commits improves the handling of whether or not the we should start the PiP or dismiss the screen.

The fourth commit hides the call button when you're already joined to the call in that room.

* It subsequently does now, however when using an unsupported deployment it will simply navigate back which isn't the case with the old implementation on develop. The user can enter https://pr2573--element-call.netlify.app/ as the base URL above the flag for testing purposes.

[github-actions]

	Warnings
⚠️	Some of the commits are missing ticket numbers. Please consider squashing all commits that don't have a tracking number.
⚠️	You seem to have made changes to views. Please consider adding screenshots.

Generated by 🚫 Danger Swift against dad9618

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 36.74699% with 105 lines in your changes missing coverage. Please review.

Project coverage is 77.82%. Comparing base (e281a3f) to head (1a2a86f).
Report is 2 commits behind head on develop.

Files	Patch %	Lines
...X/Sources/Screens/CallScreen/View/CallScreen.swift	0.00%	67 Missing ⚠️
...urces/Screens/CallScreen/CallScreenViewModel.swift	0.00%	16 Missing ⚠️
ElementX/Sources/Other/Extensions/UIView.swift	0.00%	10 Missing ⚠️
...perOptionsScreen/View/DeveloperOptionsScreen.swift	0.00%	5 Missing ⚠️
...rces/Services/ElementCall/ElementCallService.swift	0.00%	5 Missing ⚠️
.../FlowCoordinators/UserSessionFlowCoordinator.swift	50.00%	1 Missing ⚠️
...ervices/ElementCall/ElementCallConfiguration.swift	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3190      +/-   ##
===========================================
+ Coverage    77.71%   77.82%   +0.11%     
===========================================
  Files          717      718       +1     
  Lines        56478    56655     +177     
===========================================
+ Hits         43893    44093     +200     
+ Misses       12585    12562      -23     

Flag	Coverage Δ
unittests	68.39% <36.74%> (+0.05%)	⬆️

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[Velin92]

LGTM, just a few suggestions/nits

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud