[NFC] Add a method to just ask if a tuple AP vanishes under substitution

include/swift/SIL/AbstractionPattern.h

@@ -1354,6 +1354,10 @@ public:
   llvm::Optional<AbstractionPattern>
   getVanishingTupleElementPatternType() const;
 
+  /// Does this tuple type vanish, i.e. is it flattened to a singleton
+  /// non-expansion element under substitution?
+  bool doesTupleVanish() const;
+
   static AbstractionPattern
   projectTupleElementType(const AbstractionPattern *base, size_t index) {
     return base->getTupleElementType(index);

include/swift/SIL/AbstractionPatternGenerators.h

@@ -224,6 +224,11 @@ public:
     return origEltIndex == numOrigElts;
   }
 
+  /// Does the entire original tuple vanish?
+  bool doesOrigTupleVanish() const {
+    return origTupleVanishes;
+  }
+
   /// Advance to the next orig element.
   void advance() {
     assert(!isFinished());