Allow implicit conversion constraint to bridge String to NSString even

when it is the favored constraint of a disjunction.

This allows 'ns ?? "str" as String as String' to typecheck where ns is
an NSString. This does not regress the relevant test for 17962491.

<rdar://problem/20029786> Swift compiler sometimes suggests changing "as!" to "as?!"

Swift SVN r25910

lib/Sema/CSSimplify.cpp

@@ -1749,9 +1749,7 @@ ConstraintSystem::matchTypes(Type type1, Type type2, TypeMatchKind kind,
                                       TC.Context.Id_CVarArgType;
       }
       
-      if (isBridgeableTargetType && TC.getBridgedToObjC(DC, true, type1) &&
-          (kind == TypeMatchKind::ExplicitConversion ||
-           !HandlingFavoredConstraint)) {
+      if (isBridgeableTargetType && TC.getBridgedToObjC(DC, true, type1)) {
         conversionsOrFixes.push_back(ConversionRestrictionKind::BridgeToObjC);
       }
     }