Add support for overriding HLSL register/spaces

[aclysma]

When converting from GLSL to HLSL, automatic register assignment causes bindings that use multiple registers to overlap. This adds support for overriding the assignment by exposing CompilerHLSL::add_hlsl_resource_binding in spirv-cross.

Before (automatic behavior):

Texture2D<float4> shadow_map_images[32] : register(t3, space0);
TextureCube<float4> shadow_map_images_cube[16] : register(t4, space0);

This fails to compile because shadow_map_images overlaps shadow_map_images_cube in this example.

After (behavior provided by calling the added add_resource_binding which calls CompilerHLSL::add_hlsl_resource_binding:

Texture2D<float4> shadow_map_images[32] : register(t3, space0);
TextureCube<float4> shadow_map_images_cube[16] : register(t35, space0);