tests: Test load/sample status and CheckAccessFullyMapped().

The main difficulty the DXIL parser has to face here is that dx.op.textureLoad.* returns a structure with five fields. Currently we store the returned value in a vec4, which won't be enough anymore if we need to see the status field as well.

Additionally, DXIL doesn't have different variants for load and sample operations depending on whether the tiled status is needed or not, while VSIR does. In DXIL the status is always available, and the downstream can optimize it out if it's not used.

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