ASTMangler: sink fix to be more safe

My previous fix in `6f6a46f` was the correct fix in theory, but in
practice it could accidentally change the mangling of something I
haven't considered, which would break ABI with Swift 6.0

I've narrowed that fix here to only affect dependent conformances
specifically for Copyable/Escapable. The existing code in
`appendDependentProtocolConformance` would always reach a trap because
we're mangling a conformance path that ends with Copyable/Escapable.

We can assume no such symbol has been successfully been mangled before,
thanks to the pre-existing skip in `conformanceRequirementIndex`, so
there's no risk of ABI change.

rdar://135310019
(cherry picked from commit 793b46f)

Author: kavon

lib/AST/ASTMangler.cpp

@@ -4196,18 +4196,26 @@ void ASTMangler::appendAnyProtocolConformance(
       conformance.getRequirement()->isMarkerProtocol())
     return;
 
-  // While all invertible protocols are marker protocols, do not mangle them for
-  // compatability reasons. See equivalent hack in `conformanceRequirementIndex`
-  // where only invertible protocols are unconditionally skipped.
-  if (conformance.getRequirement()->getInvertibleProtocolKind())
-    return;
+  // While all invertible protocols are marker protocols, do not mangle them
+  // as a dependent conformance. See `conformanceRequirementIndex` which skips
+  // these, too. In theory, invertible conformances should never be mangled,
+  // but we *might* have let that slip by for the other cases below, so the
+  // early-exits are highly conservative.
+  const bool forInvertible =
+      conformance.getRequirement()->getInvertibleProtocolKind().has_value();
 
   if (conformingType->isTypeParameter()) {
     assert(genericSig && "Need a generic signature to resolve conformance");
+    if (forInvertible)
+      return;
+
     auto path = genericSig->getConformancePath(conformingType,
                                                conformance.getAbstract());
     appendDependentProtocolConformance(path, genericSig);
   } else if (auto opaqueType = conformingType->getAs<OpaqueTypeArchetypeType>()) {
+    if (forInvertible)
+      return;
+
     GenericSignature opaqueSignature =
         opaqueType->getDecl()->getOpaqueInterfaceGenericSignature();
     ConformancePath conformancePath =