spirv-fuzz: Add tests for fuzzer_util.cpp

[Vasniktel]

fuzzer_util.cpp has many functions that change SPIR-V module. These include Add* functions (e.g. AddVectorType and others). It would be good to have some tests for them.

[afd]

@Vasniktel Perhaps this could be split into several "good first issue"s.

[Vasniktel]

Agreed. However, there are a lot of functions in fuzzerutil::. It might be better to have a single issue for this and instead make multiple PRs to fix it. We could split PRs as follows:

• tests for all Add* functions (e.g. AddIntegerType, AddFloatType, AddFunctionType, AddVariableIdToEntryPointInterfaces, AddGlobalVariable, AddLocalVariable, AddVectorType, AddStructType)
• tests for all MaybeGet* functions (e.g. MaybeGetScalarConstant, MaybeGetCompositeConstant, MaybeGetIntegerConstant etc).
• everything else.

There are some trivial functions there, though, which we could probably ignore (e.g. FloatToWord, RepeatedUInt32PairToMap, InstructionHasNoSideEffects and maybe others).

@afd, what do you think?

[Vasniktel]

I've created to separate issues for Add* functions and MaybeGet* functions: #4178 #4179.

Thus, we can focus this issue on writing tests for the following functions:

• RemoveParameter
• UpdateFunctionType
• NewTerminatorPreservesDominationRules (maybe)