radv: add a very initial implementation of VK_EXT_graphics_pipeline_library

This experimental and very suboptimal implementation of graphics
pipeline library shouldn't be used by anyone, except for development
purposes. It's still under active development from my side. This
extension is only exposed via RADV_PERFTEST=gpl anyways.

It's very suboptimal because RADV doesn't yet support PS epilogs and
VS prologs need to be improved/reworked because GPL changed the logic
(eg. can't know the next stage when compiling a prolog). So, currently
the driver ALWAYS retains NIR shaders during libs creation and it links
and compiles in the final pipeline.

I have WIP branches for approximately everything but it looks simpler
to start merging an initial implementation in order to improve steps
by steps from main. This commit might look simple and short but I
already merged TON of preliminary work. RADV was definitely not ready
for GPL and it's still not completely fine. Expect refactoring again.

This implementation currently pass
dEQP-VK.pipeline.pipeline_library.* on NAVI21, except few feedback
creation tests due to CTS bugs.