[Sema] Don't assume member refs have base types

- Add a precondition on `doesDeclRefApplyCurriedSelf` to expect
a member decl, and rename it to make the precondition explicit.

- Don't assume that not having a base type means this isn't a member
reference, as member references to static operators don't have base
types.

Resolves SR-10843.

lib/Sema/ConstraintSystem.cpp

@@ -1222,7 +1222,7 @@ ConstraintSystem::getTypeOfMemberReference(
 
   // Check to see if the self parameter is applied, in which case we'll want to
   // strip it off later.
-  auto hasAppliedSelf = doesDeclRefApplyCurriedSelf(baseObjTy, value);
+  auto hasAppliedSelf = doesMemberRefApplyCurriedSelf(baseObjTy, value);
 
   baseObjTy = baseObjTy->getMetatypeInstanceType();
   FunctionType::Param baseObjParam(baseObjTy);