d3d12, microsoft/compiler: fix arrays of arrays and skip uniform structs
requested to merge gerddie/mesa:submit-fix-arrays-of-arrays-and-skip-uniform-structs into msclc-d3d12
Arrays of arrays of samplers are legal after all, so add support for them.
Structs still appear in the uniform list, but they are lowered, and it seems we can't really run the pass to remove unused uniforms, so while sorting the uniforms also remove the struct uniforms.