[0.6/dx] Workaround spirv-cross Limitation

[cwfitzgerald]

If a shader has a matrix as a vertex input (for things like per-instance data), spirv-cross will generate different semantics than we expect (see https://github.com/KhronosGroup/SPIRV-Cross/issues/1512). This works around the problem on both DX11 and DX12 backends. It is not implemented as efficiently as it possibly could be, but this was the easiest way to do this without really changing some functions around. Hopefully this will be resolved soon enough and this change can be removed.

I didn't bump versions as I have more fixes for both backends coming shortly.

[kvark]

Agreed to proceed as-is on matrix. bors r+

[bors[bot]]

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