1. spirv_execution_mode_id and spirv_decorate_id could support
specialization constants. The original implementation always
assume only normal frontend constants are valid. It is not true.
2. spirv_type donesn't support type_specifier as an option of
spirv_type_parameter. At present, only constant_expression is the
valid option.
- Add support of SPIR-V execution mode qualifiers.
- Add support of SPIR-V storage class qualifier.
- Add support of SPIR-V decorate qualifiers.
- Add support of SPIR-V type specifier.
- Add support of SPIR-V intruction qualifiers.
- Add support of spirv_by_reference/spirv_literal parameter qualifier.
- Add shader stage macros introduced by this extension.