Demangler: Fix printing of constrained existential types

We never updated the mangling tree to model existential types, and
NodePrinter still prints 'any P.Type' as 'P.Type' and '(any P).Type'
as 'P.Protocol'.

However, constrained existentials always printed as 'any P',
unfortunately isSimpleType() returned true and isExistentialType()
returned false, so 'any (P<Int>.Type)' and '(any P<Int>).Type' both
printed as 'any P<Int>.Type'.

Changing isSimpleType() to return false fixes this; now we print
'any (P<Int>.Type)' as 'any P<Int>.Type' and '(any P<Int>).Type'
as '(any P<Int>).Type'.

Author: slavapestov

lib/Demangling/NodePrinter.cpp

@@ -310,7 +310,6 @@ class NodePrinter {
     case Node::Kind::Pack:
     case Node::Kind::SILPackDirect:
     case Node::Kind::SILPackIndirect:
-    case Node::Kind::ConstrainedExistential:
     case Node::Kind::ConstrainedExistentialRequirementList:
     case Node::Kind::ConstrainedExistentialSelf:
     case Node::Kind::Protocol:
@@ -340,6 +339,7 @@ class NodePrinter {
     case Node::Kind::ProtocolListWithAnyObject:
       return Node->getChild(0)->getChild(0)->getNumChildren() == 0;
 
+    case Node::Kind::ConstrainedExistential:
     case Node::Kind::PackExpansion:
     case Node::Kind::ProtocolListWithClass:
     case Node::Kind::AccessorAttachedMacroExpansion: