Tooling: Migrate some tests to FileEntryRef, NFC

[dexonsmith]

Summary

Migrate to the FileEntryRef overload of SourceManager::createFileID
(using FileManager::getOptionalFileRef) in RefactoringTest.cpp and
RewriterTestContext.h.

No functionality change.

[dexonsmith]

Found another Tooling test that needed an update; adding it to this patch.

[jansvoboda11]

LGTM.

clang/unittests/Tooling/RefactoringTest.cpp

FileID createFile(llvm::StringRef Name, llvm::StringRef Content) {
     int FD;
     std::error_code EC = llvm::sys::fs::createTemporaryFile(Name, "", FD, Path);
     assert(!EC);
     (void)EC;
 
     llvm::raw_fd_ostream OutStream(FD, true);
     OutStream << Content;
     OutStream.close();
-    auto File = Context.Files.getFile(Path);
+    auto File = Context.Files.getOptionalFileRef(Path);
     assert(File);
 
     StringRef Found =
         TemporaryFiles.insert(std::make_pair(Name, std::string(Path.str())))
             .first->second;
     assert(Found == Path);
     (void)Found;
     return Context.Sources.createFileID(*File, SourceLocation(),

clang/unittests/Tooling/RewriterTestContext.h

public:
 
   ~RewriterTestContext() {}
 
   FileID createInMemoryFile(StringRef Name, StringRef Content) {
     std::unique_ptr<llvm::MemoryBuffer> Source =
         llvm::MemoryBuffer::getMemBuffer(Content);
     InMemoryFileSystem->addFile(Name, 0, std::move(Source));
 
-    auto Entry = Files.getFile(Name);
+    auto Entry = Files.getOptionalFileRef(Name);
     assert(Entry);
     return Sources.createFileID(*Entry, SourceLocation(), SrcMgr::C_User);
   }
 
   // FIXME: this code is mostly a duplicate of
   // unittests/Tooling/RefactoringTest.cpp. Figure out a way to share it.
   FileID createOnDiskFile(StringRef Name, StringRef Content) {
     SmallString<1024> Path;
     int FD;
     std::error_code EC = llvm::sys::fs::createTemporaryFile(Name, "", FD, Path);
     assert(!EC);
     (void)EC;
 
     llvm::raw_fd_ostream OutStream(FD, true);
     OutStream << Content;
     OutStream.close();
-    auto File = Files.getFile(Path);
+    auto File = Files.getOptionalFileRef(Path);
     assert(File);
 
     StringRef Found =
         TemporaryFiles.insert(std::make_pair(Name, std::string(Path.str())))
             .first->second;
     assert(Found == Path);
     (void)Found;
     return Sources.createFileID(*File, SourceLocation(), SrcMgr::C_User);