Demangler: fix a crash when re-mangling retroactive conformances

If there are multiple retroactive conformances in the mangling tree, they are put under a TypeList node.
This case was not handled by the re-mangler.
The crash shows up in an assert-build of the compiler, because the re-mangler is used for mangling verification.

rdar://problem/68467435

Author: eeckstein

lib/Demangling/Remangler.cpp

@@ -1473,8 +1473,14 @@ void Remangler::mangleImplFunctionType(Node *node) {
     mangle(PatternSubs->getChild(0));
     Buffer << 'y';
     mangleChildNodes(PatternSubs->getChild(1));
-    if (PatternSubs->getNumChildren() >= 3)
-      mangleRetroactiveConformance(PatternSubs->getChild(2));
+    if (PatternSubs->getNumChildren() >= 3) {
+      NodePointer retroactiveConf = PatternSubs->getChild(2);
+      if (retroactiveConf->getKind() == Node::Kind::TypeList) {
+        mangleChildNodes(retroactiveConf);
+      } else {
+        mangleRetroactiveConformance(retroactiveConf);
+      }
+    }
   }
 
   Buffer << 'I';

test/Demangle/Inputs/manglings.txt

@@ -329,6 +329,7 @@ _$S3BBBBf0602365061_ ---> _$S3BBBBf0602365061_
 _$S3BBBBi0602365061_ ---> _$S3BBBBi0602365061_
 _$S3BBBBv0602365061_ ---> _$S3BBBBv0602365061_
 _T0lxxxmmmTk ---> _T0lxxxmmmTk
+$s3Bar3FooVAA5DrinkVyxGs5Error_pSeRzSERzlyShy4AbcdAHO6MemberVGALSeHPAKSeAAyHC_HCg_ALSEHPAKSEAAyHC_HCg0_Iseggozo_SgWOe ---> outlined consume of @escaping @callee_guaranteed @substituted <A where A: Swift.Decodable, A: Swift.Encodable> (@guaranteed Bar.Foo) -> (@owned Bar.Drink<A>, @error @owned Swift.Error) for <Swift.Set<Abcd.Abcd.Member>>?
 $s4Test5ProtoP8IteratorV10collectionAEy_qd__Gqd___tcfc ---> Test.Proto.Iterator.init(collection: A1) -> Test.Proto.Iterator<A1>
 $s4test3fooV4blahyAA1SV1fQryFQOy_Qo_AHF ---> test.foo.blah(<<opaque return type of test.S.f() -> some>>.0) -> <<opaque return type of test.S.f() -> some>>.0
 $S3nix8MystructV1xACyxGx_tcfc7MyaliasL_ayx__GD ---> Myalias #1 in nix.Mystruct<A>.init(x: A) -> nix.Mystruct<A>