[clang] [clang][CGRecordLayout] Remove dependency on isZeroSize (PR #96422)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

This is roughly what I expected the patch to look like.  Maybe consider adding a couple small wrapper functions around isEmptyRecord/isEmptyField to simplify the uses (and so we can use a name that indicates why the checks exist).

https://github.com/llvm/llvm-project/pull/96422