Avoid boxing in DeferredDisposableLifetime (#79778)

* Avoid boxing in DeferredDisposableLifetime

* Move `typeof` lookup behind the if check

Author: MihaZupan

src/libraries/System.Private.CoreLib/src/System/Threading/DeferredDisposableLifetime.cs

@@ -50,7 +50,8 @@ public bool AddRef()
                 int oldCount = Volatile.Read(ref _count);
 
                 // Have we been disposed?
-                ObjectDisposedException.ThrowIf(oldCount < 0, this);
+                if (oldCount < 0)
+                    throw new ObjectDisposedException(typeof(T).ToString());
 
                 int newCount = checked(oldCount + 1);