Normalise the incoming vkd3d_shader_instruction IR to the shader model 6 pattern where only one patch constant function is emitted. This allows generation of a single patch constant function in SPIR-V.
-- v7: vkd3d-shader/normalise: Insert hull shader control point input declarations if no control point phase is defined. vkd3d-shader/normalise: Normalise control point phase output registers to include the control point id. vkd3d-shader: Introduce an internal sm6 signature structure. vkd3d-shader/spirv: Move the function declaration from spirv_compiler_begin_shader_phase() to spirv_compiler_enter_shader_phase(). vkd3d-shader/spirv: Remove the hull shader phase array. vkd3d-shader/normalise: Merge all shader IR fork and join phases into a single phase. vkd3d-shader/normalise: Introduce a normaliser structure.