[Async Refactoring] Convert data structure storing continuation resume args to std::vector

The `std::vector` keeps its elements alive. Currently, we might be accessing uninitalized memory if the call of `callArgs(CE)` (which owns its elements in case there is a single element) goes out of scope before `Args`.

Author: ahoppen

lib/IDE/Refactoring.cpp

@@ -6634,7 +6634,7 @@ class AsyncConverter : private SourceEntityWalker {
            "TopHandler's completion handler");
     assert(Scopes.back().isWrappedInContination());
 
-    ArrayRef<Expr *> Args;
+    std::vector<Expr *> Args;
     StringRef ResumeArgumentLabel;
     switch (TopHandler.getHandlerType()) {
     case HandlerType::PARAMS: {