Create a 'mesa-next' package that tracks latest stable Mesa release

The package should track the latest stable major/minor releases, and build only drivers used by mobile devices[1]. This was inspired by my work on !236 (merged)

1: This is necessary because AMD gpu drivers require newer versions of llvm, and updating llvm is currently one of the main reasons why Alpine cannot keep up with the latest stable Mesa release. I'm unaware of any mobile devices that use AMD graphics..