[Mesa-dev] Indirect fixes for Samplers v3

[Timothy Arceri]

The following patch series fixes the indirect sampler indexing piglit tests
 /tests/spec/arb_gpu_shader5/execution/sampler_array_indexing/* for nir.
It also takes steps toward removing the use of the UniformHash table.

There are no piglit regressions and I've also sent a couple more meaner
indirect tests to the piglit list [1].

Patch 6 is a related clean-up that is optional but gets us a step closer to
removing the UniformHash hash table.

V3: updates based on feedback from Jason, introduced patch 2 to assign
uniforms hidden uniforms their final slot ids *before* storage allocation.
Update patch 3 to make sure the location is stored for every stage not
just the first one with the uniform.

V2: nir change passes validation in debug build

[1] https://patchwork.freedesktop.org/patch/58063/