Second part of !50.
-- v4: vkd3d-shader/hlsl: Add field-level documentation to struct hlsl_scope. vkd3d-shader/hlsl: Add field-level documentation to function structs. vkd3d-shader/hlsl: Add field-level documentation to struct hlsl_buffer. vkd3d-shader/hlsl: Add documentation to small hlsl.h structs. vkd3d-shader/hlsl: Add field-level documentation to struct hlsl_deref.