radv: add support for VK_KHR_fragment_shading_rate on GFX10.3+
Based on !7795 (merged), !7835 (closed), !7892 (merged) and !7815 (merged)
Marked as draft since there is still some failures with MSAA8x and SampleMaskIn, the feature could be disabled until it's fixed properly though.
EDIT: gl_SampleMaskIn failures are fixed, it pass CTS.