Goes atop MR 403 and 388. The last eight commits belong to this MR (to be split).
-- v6: vkd3d-shader/dxil: Implement the DXIL EXTRACTVAL instruction. vkd3d-shader/spirv: Support scalar swizzle of vector SSA registers. vkd3d-shader/dxil: Implement DX instruction CBufferLoadLegacy. vkd3d-shader/dxil: Implement DX instruction CreateHandle. vkd3d-shader: Clone descriptor scan info from struct vkd3d_shader_desc. vkd3d-shader/dxil: Read CBV descriptors. vkd3d-shader/dxil: Validate the descriptor list metadata nodes. vkd3d-shader/spirv: Align constant buffer sizes to 16 bytes.