clang-format: Allow include of clangFormat.h in managed context

[mxbOctasic]

Summary

Including VirtualFileSystem.h in the clangFormat.h indirectly includes <atomic>.
This header is blocked when compiling with /clr.
I added a forward declaration of vfs::FileSystem in clangFormat.h and moved the include to clangFormat.cpp.

[djasper]

Looks good.

include/clang/Format/Format.h

30

nit: Remove this empty line.

[mxbOctasic]

Removed empty line.

include/clang/Format/Format.h

 /// Various functions to configurably format source code.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_FORMAT_FORMAT_H
 #define LLVM_CLANG_FORMAT_FORMAT_H
 
 #include "clang/Basic/LangOptions.h"
-#include "clang/Basic/VirtualFileSystem.h"
 #include "clang/Tooling/Core/Replacement.h"
 #include "llvm/ADT/ArrayRef.h"
 #include <system_error>
 
 namespace clang {
 
 class Lexer;
 class SourceManager;
 class DiagnosticConsumer;
 
+namespace vfs {
+class FileSystem;
+}
+
 namespace format {
 
 enum class ParseError { Success = 0, Error, Unsuitable };
 class ParseErrorCategory final : public std::error_category {
 public:
   const char *name() const LLVM_NOEXCEPT override;
   std::string message(int EV) const override;
 };

lib/Format/Format.cpp

 #include "ContinuationIndenter.h"
 #include "TokenAnnotator.h"
 #include "UnwrappedLineFormatter.h"
 #include "UnwrappedLineParser.h"
 #include "WhitespaceManager.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Basic/VirtualFileSystem.h"
 #include "clang/Lex/Lexer.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Regex.h"
 #include "llvm/Support/YAMLTraits.h"
 #include <queue>