[TBAA] Add verifier for tbaa.struct metadata (#86709)

Adds logic to the IR verifier that checks whether !tbaa.struct nodes are
well-formed. That is, it checks that the operands of !tbaa.struct nodes
are in groups of three, that each group of three operands consists of
two integers and a valid tbaa node, and that the regions described by
the offset and size operands are non-overlapping.

PR: https://github.com/llvm/llvm-project/pull/86709