[clang] [APINotes] Upstream APINotesWriter (PR #65187)

[Egor Zhdan via cfe-commits]

================
@@ -33,6 +33,7 @@ class APINotesWriter::Implementation {
   /// Mapping from strings to identifier IDs.
   llvm::StringMap<IdentifierID> IdentifierIDs;
 
+public:
----------------
egorzhdan wrote:

Reverted this part of the change by making `APINotesWriter` a friend class of `Implementation`

https://github.com/llvm/llvm-project/pull/65187