Less Mesa dependency : Make packages dependent on OpenGL/libglvnd or libdrm instead.

Mesa is big and takes time to build and causes a cascade in rebuilds for the dependencies, when those dependencies only need OpenGL headers and the vendor-neutral dispatch library to link against. This could possibly improve concurrency in the Buildstream build (not waiting for Mesa).

I've chosen not to go too extreme and left some of the dependencies like gstreamer plugins, xwayland, sdl2 and the mutter compositor as they touch libgbm directly, which comes with Mesa. I'd like to revisit some to verify though especially mutter and gstreamer.

This also removes SDL2 dependency on Pipewire + GStreamer as these are just for the tests/examples (SDL2 needs Mesa for the KMS/DRM backend, which uses libgbm directly).

Fixes #130 (closed)