Goes atop !459. The last six commits belong to this MR.
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v5: vkd3d-shader/dxil: Implement the DXIL LOAD instruction.
vkd3d-shader/dxil: Implement the DXIL GEP instruction.
vkd3d-shader/dxil: Support global variable initialisers.
vkd3d-shader/dxil: Introduce a value type for immediate constant buffers.
vkd3d-shader/dxil: Implement default address space global variables.
vkd3d-shader: Delete unused struct list from struct vkd3d_shader_indexable_temp.
https://gitlab.winehq.org/wine/vkd3d/-/merge_requests/471