[DirectX] Array GEPs need two indices (#142853)
partially fixes #142836
- Update DXILFlattenArrays.cpp GEPs to use two indicies since they are
array GEPs
- Update flatten test cases
- This change reduces dxv bitcast validation errors by 364 (Total now is
1070x)
- This change reduces dxv out of bounds validation errors by 124 (Total
is now 24)
- We are also able to successfully compile 4 more shaders
