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

[VASU SHARMA via cfe-commits]

vasu-the-sharma wrote:

> > I've been working on the changes and wanted to share the IR comparison to make sure we're on the right track.
> 
> @vasu-the-sharma, please clean up your write-up to focus on what's new compared to what the PR already proposes.

Done. The new change is the `LHS` check in `CGExprAgg.cpp`:
```
- LValue LHS = CGF.EmitLValue(E->getLHS());
+ LValue LHS = CGF.EmitCheckedLValue(E->getLHS(), CodeGenFunction::TCK_Store);
```

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