This commit adds initial support for SPIR-V OpSpecConstantOp
instruction. The following is introdcued:
- A new spv.specConstantOperation operation consisting of a single
region and of 2 operations within that regions (more details in the
docs of the op itself).
- A new spv.yield instruction that acts a terminator for
For now, the generic form of the new op is supported (i.e. no custom
parsing or printing). This will be done in a follow up patch.