[clang] Deprecate `DirectoryEntry::getName()`

[jansvoboda11]

Summary

This finally officially deprecates DirectoryEntry::getName(). I checked no usages remain in targets built by any of check-clang, check-clang-tools, check-clang-extra. There are probably some remaining usages in places like LLDB and other clients. This will give them a chance to transition to DirectoryEntryRef::getName() before we remove the function altogether.

Depends on D151922.

clang/include/clang/Basic/DirectoryEntry.h

class DirectoryEntry {
   DirectoryEntry &operator=(const DirectoryEntry &) = delete;
   friend class FileManager;
   friend class FileEntryTestHelper;
 
   // FIXME: We should not be storing a directory entry name here.
   StringRef Name; // Name of the directory.
 
 public:
+  LLVM_DEPRECATED("Use DirectoryEntryRef::getName() instead.", "")
   StringRef getName() const { return Name; }
 };
 
 /// A reference to a \c DirectoryEntry  that includes the name of the directory
 /// as it was accessed by the FileManager's client.
 class DirectoryEntryRef {
 public:
   const DirectoryEntry &getDirEntry() const { return *ME->getValue(); }