[cxx-interop] NFC: Move a header from include into lib

CXXMethodBridging.h isn't supposed to be used outside of ClangImporter, so let's keep it inside of ClangImporter's implementation.

lib/ClangImporter/CXXMethodBridging.h

@@ -4,9 +4,10 @@
 #include "swift/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
 #include "llvm/ADT/StringRef.h"
-
 #include <string>
+
 namespace swift {
+
 struct CXXMethodBridging {
   enum class Kind { unknown, getter, setter, subscript };
 
@@ -165,5 +166,7 @@ private:
            loweredName == "get" || loweredName == "set";
   }
 };
+
 } // namespace swift
+
 #endif // SWIFT_CXXMETHODBRIDGING_H

lib/ClangImporter/ImportDecl.cpp

@@ -15,6 +15,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "CFTypeInfo.h"
+#include "CXXMethodBridging.h"
 #include "ClangDerivedConformances.h"
 #include "ImporterImpl.h"
 #include "SwiftDeclSynthesizer.h"
@@ -50,7 +51,6 @@
 #include "swift/Basic/Statistic.h"
 #include "swift/Basic/StringExtras.h"
 #include "swift/Basic/Version.h"
-#include "swift/ClangImporter/CXXMethodBridging.h"
 #include "swift/ClangImporter/ClangImporter.h"
 #include "swift/ClangImporter/ClangImporterRequests.h"
 #include "swift/ClangImporter/ClangModule.h"

lib/ClangImporter/SwiftDeclSynthesizer.cpp

@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "CXXMethodBridging.h"
 #include "SwiftDeclSynthesizer.h"
 #include "swift/AST/ASTMangler.h"
 #include "swift/AST/AttrKind.h"
@@ -20,7 +21,6 @@
 #include "swift/AST/Pattern.h"
 #include "swift/AST/Stmt.h"
 #include "swift/Basic/Assertions.h"
-#include "swift/ClangImporter/CXXMethodBridging.h"
 #include "clang/AST/Mangle.h"
 #include "clang/Sema/DelayedDiagnostic.h"