spirv-fuzz: ReplaceIrrelevantId can introduce undefined behaviour

An index operand in `OpAccessChain` can be irrelevant. Thus, `TransformationReplaceIrrelevantId` can replace it with some other value. However, the new value may no longer be a valid index into the pointer if the latter points to array, matrix or vector. This causes assertion failures in spirv-opt that look like this:
```
error: line 32: Array access is out of bounds, array size is 8, but access index is 9
%937 = OpCompositeExtract %float %951 9 0
```
Here, `OpAccessChain` was replaced with `OpCompositeExtract` in `convert-local-access-chains` pass.

Start with TransformationReplaceIrrelevantId and the convert-local-access-chains pass mentioned in the report. Reproduce the failing spirv-opt assertion using an OpAccessChain whose index is replaced, then verify that relevant array, matrix, and vector accesses remain valid and no out-of-bounds assertion occurs.

Written by the indexing model from the issue text.