[Flatpak SDK] Enable openh264 GStreamer plugin

[philn]

265bd1b

[Flatpak SDK] Enable openh264 GStreamer plugin
https://bugs.webkit.org/show_bug.cgi?id=244158

Reviewed by Adrian Perez de Castro.

This encoder claims to support the constrained-high profile whereas x264enc doesn't, so this encoder
will be used for some WebRTC layout tests requiring that profile.

* Tools/buildstream/elements/sdk/gst-plugins-bad.bst:
* Tools/buildstream/elements/sdk/libopenh264.bst:
* Tools/buildstream/patches/gst-plugins-bad-openh264-Register-debug-categories-earlier.patch: Added.
* Tools/buildstream/patches/gst-plugins-bad-openh264enc-Fix-constrained-high-encoding.patch: Added.

Canonical link: https://commits.webkit.org/253627@main

5303dd7

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 🧪 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-debug	✅ 🛠 gtk	✅ 🛠 wincairo
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🛠 mac-AS-debug	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 api-mac	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-wk1
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2
	✅ 🛠 watch	✅ 🧪 mac-AS-debug-wk2
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim	✅ 🧪 mac-wk2-stress

[webkit-early-warning-system]

5303dd7

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 🧪 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-debug	✅ 🛠 gtk	✅ 🛠 wincairo
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🛠 mac-AS-debug	✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 api-mac	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-wk1
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2
	✅ 🛠 watch	✅ 🧪 mac-AS-debug-wk2
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim	✅ 🧪 mac-wk2-stress

[webkit-commit-queue]

Committed 253627@main (265bd1b): https://commits.webkit.org/253627@main

Reviewed commits have been landed. Closing PR #3503 and removing active labels.