[clang] [Clang][objectsize] Generate object size calculation for sub-objects (PR #86858)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I agree you want to look through some casts... but I'd like to see a check of `getCastKind()` to ensure the cast you're looking through is a cast you're expecting to see.  Skipping over CK_BitCast should be fine; I'm concerned you'll end up skipping over something that actually affects the pointer value like CK_DerivedToBase.

https://github.com/llvm/llvm-project/pull/86858