[MLIR][SPIRV] Add (de-)serialization support for SpecConstantOpeation.

This commit adds support for (de-)serializing SpecConstantOpeation. One
thing worth noting is that during deserialization, we assign a fake ID to
enclosed ops inside SpecConstantOpeation. We need to do this in order
for deserialization logic to properly update ID to value map and to
later reference the created value from the sibling 'spv::YieldOp'.

Reviewed By: antiagainst

Differential Revision: https://reviews.llvm.org/D93591