Statically link libSDL2 against libpipewire, like all of the other dependencies of SDL2.
This finally makes SDL2 explicitly depend on all of its external deps, which will make easier to track ABI changes for SDL2 rebuilds and keep track of features that are enabled in our SDL2 build.
Depends on D14113.

Checked that sdl2, pipewire and ffmpeg are co-installable and there are no cycle dependencies between them.