Element Call integration into Mainline Apps

[fkwp]

This is an epic issue. List of individual issues is below:

This epic lists the tickets to integrate Element Call (which is based on WebRTC) into the mainline applications Element Web, Element Android, and Element iOS.

Recent web-browser engines comprise a decent WebRTC implementation as well as (audio / video) media handling. On top of that stack Element Call was developed implementing scalable decentralised E2EE group voice and video calling (MSC3401). For the sake of time, MSC3401 is integrated into the mainline applications as a widget, but sharing the host app's Matrix client, on all 3 platforms embedding Element Call.

Note the native integration MSC3401 is at the current point in time out of scope.

• [ ] https://github.com/matrix-org/matrix-spec-proposals/pull/3819
• [x] https://github.com/matrix-org/matrix-js-sdk/issues/2552
• [x] https://github.com/vector-im/element-web/issues/22964
• [x] https://github.com/vector-im/element-call/issues/330
• [x] https://github.com/vector-im/element-call/issues/486
• [x] https://github.com/vector-im/element-call/issues/558
• [x] https://github.com/matrix-org/matrix-js-sdk/issues/2589
• [x] https://github.com/vector-im/element-web/issues/23107
• [ ] https://github.com/vector-im/element-web/issues/23453
• [x] https://github.com/vector-im/element-web/issues/23335
• [x] https://github.com/vector-im/element-web/issues/23494
• [x] https://github.com/matrix-org/matrix-react-sdk/pull/9423
• [x] https://github.com/matrix-org/matrix-react-sdk/pull/9424
• [x] https://github.com/matrix-org/matrix-react-sdk/pull/9426
• [x] https://github.com/vector-im/element-web/issues/23335