vkd3d-shader/d3dbc: Compile HLSL to d3dbc through vsir, part 1.

For now just writing the declaration instructions from struct vsir_program input/output signatures created from the HLSL IR externs, some more changes to stop relying on hlsl_ctx, and some scaffolding before commencing the translation from struct hlsl_ir_node values to struct vkd3d_shader_instruction values.

Currently there is no way of storing the uniforms reflection data in the struct vsir_program, so it was suggested for the CTAB blob to be expected independently in the new d3dbc_compile(). If we want to support translations from other input formats directly to d3dbc, we could introduce something like struct vkd3d_shader_scan_descriptor_info1 for uniforms or making a function for these input formats to write a CTAB blob directly.