NFC: Move GenericSelectionExpr dump to NodeDumper

[aaron.ballman]

LGTM!

include/clang/AST/TextNodeDumper.h

#include "clang/AST/AttrTextNodeDump.inc"
   void VisitDeclRefExpr(const DeclRefExpr *Node);
   void VisitPredefinedExpr(const PredefinedExpr *Node);
   void VisitCharacterLiteral(const CharacterLiteral *Node);
   void VisitIntegerLiteral(const IntegerLiteral *Node);
   void VisitFixedPointLiteral(const FixedPointLiteral *Node);
   void VisitFloatingLiteral(const FloatingLiteral *Node);
   void VisitStringLiteral(const StringLiteral *Str);
   void VisitInitListExpr(const InitListExpr *ILE);
+  void VisitGenericSelectionExpr(const GenericSelectionExpr *E);
   void VisitUnaryOperator(const UnaryOperator *Node);
   void VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr *Node);
   void VisitMemberExpr(const MemberExpr *Node);
   void VisitExtVectorElementExpr(const ExtVectorElementExpr *Node);
   void VisitBinaryOperator(const BinaryOperator *Node);
   void VisitCompoundAssignOperator(const CompoundAssignOperator *Node);
   void VisitAddrLabelExpr(const AddrLabelExpr *Node);
   void VisitCXXNamedCastExpr(const CXXNamedCastExpr *Node);

lib/AST/ASTDumper.cpp

dumpChild([=] {
     const TypeSourceInfo *TSI = A.getTypeSourceInfo();
     if (TSI)
       dumpTypeAsChild(TSI->getType());
     dumpStmt(A.getExpr());
   });
 }
 
 void ASTDumper::VisitGenericSelectionExpr(const GenericSelectionExpr *E) {
-  if (E->isResultDependent())
-    OS << " result_dependent";
   dumpStmt(E->getControllingExpr());
   dumpTypeAsChild(E->getControllingExpr()->getType()); // FIXME: remove
 
   for (unsigned I = 0, N = E->getNumAssocs(); I != N; ++I) {
     Visit(E->getAssociation(I));
   }
 }
 

lib/AST/TextNodeDumper.cpp

 
 void TextNodeDumper::VisitInitListExpr(const InitListExpr *ILE) {
   if (auto *Field = ILE->getInitializedFieldInUnion()) {
     OS << " field ";
     dumpBareDeclRef(Field);
   }
 }
 
+void TextNodeDumper::VisitGenericSelectionExpr(const GenericSelectionExpr *E) {
+  if (E->isResultDependent())
+    OS << " result_dependent";
+}
+
 void TextNodeDumper::VisitUnaryOperator(const UnaryOperator *Node) {
   OS << " " << (Node->isPostfix() ? "postfix" : "prefix") << " '"
      << UnaryOperator::getOpcodeStr(Node->getOpcode()) << "'";
   if (!Node->canOverflow())
     OS << " cannot overflow";
 }
 
 void TextNodeDumper::VisitUnaryExprOrTypeTraitExpr(