Since the sort index is just a convenience field it is more
appropriate to only set it where it is required, instead of
requiring all frontends and passes to retain sensible values for
it.
This way the same shader is always dumped to the same path and when
launching the same program over and over we avoid both creating new
copies of the same file each time and overwriting different dumped
shaders.
For tpf shader this would previously be a pointer into the original
shader code, and for d3dbc shaders we'd use static strings.
Unfortunately the dxil parser creates shader signatures where these
are pointers to metadata strings, and those go away when we call
sm6_parser_cleanup().
We could conceivably store a flag in the shader signature to indicate
whether shader_signature_cleanup()/vkd3d_shader_free_shader_signature()
should free the "semantic_name" field. It'd be a little ugly, and seems
unlikely to be worth it, but I'd be willing to be convinced.
We want to be able to remap input signatures based on the signature index, but
signature normalization both reorders the signature, and requires the old
register index, so add a new field for this.
