Feat: Streaming video elements via webrtc

[Juice10]

Video elements using blob: urls and video.srcObject = can be captured via webrtc. Tweak canvas-webrtc-plugin to support video streaming as well as canvas streams.

TODO:

• [ ] rename canvas-webrtc-plugin to rrweb-webrtc-plugin
• [ ] ~support YouTube streaming~
• [x] support Loom streaming

[eoghanmurray]

Does the newer asset stuff of #1239 make this moot?

[Juice10]

No this would be a far more efficient way to live stream video elements based on users' (upload) bandwidth as webrtc changes the quality to match bandwidth