[AST] Move ModuleEntity from libIDE to libAST so that the ASTPrinter can use it.

Swift SVN r23680

lib/IDE/ModuleInterfacePrinting.cpp

@@ -57,7 +57,7 @@ private:
   void printTypeRef(const TypeDecl *TD, Identifier Name) override {
     return OtherPrinter.printTypeRef(TD, Name);
   }
-  void printModuleRef(const Module *Mod, Identifier Name) override {
+  void printModuleRef(ModuleEntity Mod, Identifier Name) override {
     return OtherPrinter.printModuleRef(Mod, Name);
   }