vkd3d-shader/dxil: Do not use relative component indices for output dst param write masks.

Component indices for DXIL output stores are relative to the first component of the signature element mask. The I/O normaliser does not emit relative write masks since c571a45e. TPF output masks usually start at component 0 because sysval and non-sysval elements do not share the same register, and therefore cannot result in different declarations where one starts at a non-zero component. However, this rule is broken for tessellation factors, where the factor occupies x and another element can use yzw. The DXIL parser must conform to the older pattern instead of the reverse.

The parser change has no effect on code emitted by the backend, but without this change it fails to meet the condition mentioned in the comment in spirv_compiler_emit_store_scalar().

We now have a situation where VSIR I/O src params use relative component indices, i.e. they are normalised to the SM 6 pattern, but dst params are not, so it would make sense for a future MR to remove the src param normalisation.