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

[Hubert Tong via cfe-commits]

hubert-reinterpretcast wrote:

> **UBSan call count (for test_lhs + test_rhs + test_both):**
> 
>     * Without change: 3 (RHS checks only)
> 
>     * With change: 5 (LHS + RHS checks)

I'm not seeing any `test_rhs` and `test_both`. Based on previous review comments, we would like to avoid `test_both` as having a bad cost/benefit ratio.

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