spirv-fuzz: Support more synonyms in TransformationAddSynonym

Consider supporting more types of synonymous instructions in `TransformationAddSynonym` (e.g. `a = min(a, a)`, `a = a xor 0` etc). Take a look at the protobuf's message for `TransformationAddSynonym` for more details.

Start with the protobuf message for TransformationAddSynonym and trace its implementation and dispatch entry point. Determine how existing synonymous instructions are represented, then define support for cases such as a = min(a, a) and a = a xor 0. Done means the requested synonym forms are accepted and covered by the relevant validation or transformation checks.

Written by the indexing model from the issue text.