[clang] NFCI: Use DirectoryEntryRef in Module::Directory

This patch changes the type of `Module::Directory` from `const DirectoryEntry *` to (essentially) `Optional<DirectoryEntryRef>` in order to remove uses of the deprecated `DirectoryEntry::getName()`.

Depends on D127651.

Reviewed By: bnbarham

Differential Revision: https://reviews.llvm.org/D127654

GitOrigin-RevId: 32d6f3cfd90b90321e84477b2bd353afbf9876ea
2 files changed