build-aux: Replace Flatpak modules with pre-compiled dependencies

[tytan652]

Description

Important

This PR relies on https://github.com/tytan652/obs-deps-bst, the PR is also meant to discuss including the BuildStream-based project under the obsproject org.

This PR is x86_64 only, if it gets approved, #9979 will be refactored with aarch64 tarballs and I will try to work on documenting obs-deps-bst.

To reduce compile time and prepare for aarch64 support, dependencies compilation except CEF is moved to a BuildStream project junctionned with Freedesktop SDK.

The BuildStream project is configured to build dependencies in a Flatpak-like environment.

Motivation and Context

Move away dependency compile time, in an aarch64 context it moves away 6 hours of build time to another repo with ~3 hours of build time* without cache.
So only the CEF wrapper and OBS have to be built on this repo CI, so ~1h IIRC for aarch64 without cache.

*Build time is reduced since BuildStream tries to build elements in parallel when possible even with QEMU emulation.

Also on obs-deps-bst side, sources are cached so outage of independent git remote is not an issue if cached.

How Has This Been Tested?

Types of changes

• Tweak (non-breaking change to improve existing functionality)
• Performance enhancement (non-breaking change which improves efficiency)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.