Use function-local StackingAllocator for EnC added methods (#26256)

As adding EnC methods happens on the Debugger Thread, there's no managed Thread object from which to obtain the cached StackingAllocator. Instead, just use a function-local StackingAllocator.

Author: hoyosjs

src/vm/class.cpp

@@ -604,12 +604,16 @@ HRESULT EEClass::AddMethod(MethodTable * pMT, mdMethodDef methodDef, RVA newRVA,
     // Get the new MethodDesc (Note: The method desc memory is zero initialized)
     MethodDesc *pNewMD = pChunk->GetFirstMethodDesc();
 
-    ACQUIRE_STACKING_ALLOCATOR(pStackingAllocator);
 
     // Initialize the new MethodDesc
+    
+     // This method runs on a debugger thread. Debugger threads do not have Thread object that caches StackingAllocator.
+     // Use a local StackingAllocator instead.
+    StackingAllocator stackingAllocator;
+
     MethodTableBuilder builder(pMT,
                                pClass,
-                               pStackingAllocator,
+                               &stackingAllocator,
                                &dummyAmTracker);
     EX_TRY
     {