[Metadata] Add TBAA struct metadata to AAMDNode
Make AAMDNodes' getAAMetadata() and setAAMetadata() to take !tbaa.struct
into account as well as !tbaa. This impacts llvm.org/pr42022.
This is a temprorary fix needed to keep !tbaa.struct tag by SROA pass.
New field TBAAStruct should be deleted when !tbaa tag replaces !tbaa.struct.
Merging two !tbaa.struct's to one is conservatively considered to be nullptr
(giving MayAlias) -- this could be enhanced, but relying on the said future
Reviewers: RKSimon, spatel, vporpo
Subscribers: hiraditya, kosarev, llvm-commits
Differential Revision: https://reviews.llvm.org/D70924