[CSFix] Add a fix to allow value pack expansions without pack references

Situations like `repeat x` where `x` is `Int` where pack expansion
expression doesn't have any pack references.

lib/Sema/CSSimplify.cpp

@@ -14803,6 +14803,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::AllowTupleLabelMismatch:
   case FixKind::AddExplicitExistentialCoercion:
   case FixKind::DestructureTupleToMatchPackExpansionParameter:
+  case FixKind::AllowValueExpansionWithoutPackReferences:
     llvm_unreachable("handled elsewhere");
   }