This MR replaces `vkd3d_shader_register.immconst_type` with `vkd3d_shader_register.dimension` which is intended for all register types and not just immconsts.
This dimension is parsed in tpf.c, and initialized according to the register type in d3dbc.c.
Having this field in vkd3d_shader_register allows us to avoid hardcoding special cases for the register dimensions when writing sm4 bytecode (e.g. for the sampler src register in gather instructions). Also, it allows for some fixes to d3d_asm.c, which are introduced in part 2 (https://gitlab.winehq.org/fcasas/vkd3d/-/commits/add_vkd3d_reg_dim).
-- v2: vkd3d-shader: Initialize registers using shader_register_init(). vkd3d-shader: Make shader_register_init() extern. vkd3d-shader/d3dbc: Initialize register dimension for all register types. vkd3d-shader/tpf: Parse register dimension for all register types. vkd3d-shader: Turn vkd3d_shader_register.immconst_type into vkd3d_shader_register.dimension.