Multiple fork and join phases are eliminated. Signature elements are merged where required, and all input/output parameters are rewritten.
-- v3: 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/spirv: Merge all shader IR fork and join phases into a single phase.