[clang] [UBSAN] add null and alignment checks for aggregates and update coverage (PR #175032)

[VASU SHARMA via cfe-commits]

vasu-the-sharma wrote:

<img width="1727" height="302" alt="image" src="https://github.com/user-attachments/assets/c6ec0f1a-1149-452b-b458-22afface532c" />


https://github.com/llvm/llvm-project/pull/175032