Enable PipeWire capturer by default

[vchernin]

Now that Element 1.8 is released (should be merged here in element-hq/element-web#201), screen sharing now works in 1:1 calls. Group calls (embedded Jitsi) are still broken due to element-hq/element-web#150.

However, for Wayland we need to pass --enable-features=WebRTCPipeWireCapturer at runtime. This could be done in the desktop file or maybe with zypak. As a workaround you can do flatpak run im.riot.Riot --enable-features=WebRTCPipeWireCapturer.

I tried to build locally but apparently flatpak-builder on Fedora 34 Silverblue for me is cursed with OOM errors (this has happened elsewhere). I'll open a PR after element-hq/element-web#201 is merged.

We can also remove PipeWire 0.2.7 from the manifest since Element now ships Electron 13 (which works with 0.3.x in the runtime).

I also noticed Element experiences a similar screen sharing with PipeWire issue as Jitsi meet electron (nothing to do with Element, but another electron 13 app).

[vchernin]

Opened an issue to enable the flag at buildtime as that will help .DEB users out too: element-hq/element-web#18607

[vchernin]

Open PR: element-hq/element-desktop#256

[vchernin]

This is now fixed upstream, and should work out of the box in the next Element release. See element-hq/element-web#18607 (comment)

I'll open a followup PR here to remove the old PipeWire and remove the metainfo mention of PipeWire (it is redundant now).

[vchernin]

Follow up issue: element-hq/element-desktop#853