vkd3d-shader/hlsl: Interstage signature optimization, part 1.

Interstage signature optimization is required to fix CW Bug 24073, Eastward.

Native compiler optimizes pixel shader output and vertex shader input signatures in order to use less registers.

This first part contains just the tests. Tests in 1/3 are not really testing the signatures and are just for documenting purposes. Testing them directly would require adding reflection to the shader runner.

Two complex tests to hlsl_d3d12.c are added in 2/3 and 3/3, the one in 3/3 includes arrays within the signature.

The following patches are in my eastward2 branch.