[clang] [UBSAN] [FC] add null, alignment and array-bounds checks (PR #190739)

[Hubert Tong via cfe-commits]

https://github.com/hubert-reinterpretcast commented:

There is no need to mark this PR "FC" as opposed to "NFC".

Also, why did the scope of this reduce from handling both the LHS and RHS (in llvm/llvm-project#164548) to handling just the RHS?

https://github.com/llvm/llvm-project/pull/190739