[clang][lex] NFC: Use FileEntryRef in PreprocessorLexer::getFileEntry()

[jansvoboda11]

Summary

This patch changes the return type of PreprocessorLexer::getFileEntry() so that its clients may stop using the deprecated APIs of FileEntry.

clang/include/clang/Lex/PreprocessorLexer.h

public:
 
   /// Number of SLocEntries before lexing the file.
   unsigned getInitialNumSLocEntries() const {
     return InitialNumSLocEntries;
   }
 
   /// getFileEntry - Return the FileEntry corresponding to this FileID.  Like
   /// getFileID(), this only works for lexers with attached preprocessors.
-  const FileEntry *getFileEntry() const;
+  OptionalFileEntryRefDegradesToFileEntryPtr getFileEntry() const;
 
   /// Iterator that traverses the current stack of preprocessor
   /// conditional directives (\#if/\#ifdef/\#ifndef).
   using conditional_iterator =
       SmallVectorImpl<PPConditionalInfo>::const_iterator;
 
   conditional_iterator conditional_begin() const {
     return ConditionalStack.begin();

clang/lib/Lex/PreprocessorLexer.cpp

else
     PP->Lex(FilenameTok);
 
   // We should have obtained the filename now.
   ParsingFilename = false;
 }
 
 /// getFileEntry - Return the FileEntry corresponding to this FileID.  Like
 /// getFileID(), this only works for lexers with attached preprocessors.
-const FileEntry *PreprocessorLexer::getFileEntry() const {
-  return PP->getSourceManager().getFileEntryForID(getFileID());
+OptionalFileEntryRefDegradesToFileEntryPtr
+PreprocessorLexer::getFileEntry() const {
+  return PP->getSourceManager().getFileEntryRefForID(getFileID());
 }

clang/lib/Sema/SemaCodeComplete.cpp

void Sema::CodeCompleteIncludedFile(llvm::StringRef Dir, bool Angled) {
 
   // Finally with all our helpers, we can scan the include path.
   // Do this in standard order so deduplication keeps the right file.
   // (In case we decide to add more details to the results later).
   const auto &S = PP.getHeaderSearchInfo();
   using llvm::make_range;
   if (!Angled) {
     // The current directory is on the include path for "quoted" includes.
-    auto *CurFile = PP.getCurrentFileLexer()->getFileEntry();
+    const FileEntry *CurFile = PP.getCurrentFileLexer()->getFileEntry();
     if (CurFile && CurFile->getDir())
       AddFilesFromIncludeDir(CurFile->getDir()->getName(), false,
                              DirectoryLookup::LT_NormalDir);
     for (const auto &D : make_range(S.quoted_dir_begin(), S.quoted_dir_end()))
       AddFilesFromDirLookup(D, false);
   }
   for (const auto &D : make_range(S.angled_dir_begin(), S.angled_dir_end()))
     AddFilesFromDirLookup(D, false);