Quit test drivers through ApplicationExit and free test resources

Adds tests for freeing the temporary ext_resource sub-scene instance; the
animated foreground tests dispose their frame textures.

test_suites/doc_shots/src/DocShotsDriver.cs

@@ -409,7 +409,7 @@ namespace Cthangover.Mods.Dialog.DocShots
         {
             index = -1;
             GameLogger.Log("TEST", $"[TEST_RESULT] name=doc_shots passed={passed} failed={failures.Count}");
-            GetTree().Quit(failures.Count == 0 ? 0 : 1);
+            Cthangover.Core.Bootstrap.ApplicationExit.Quit(GetTree(), failures.Count == 0 ? 0 : 1);
         }
     }
 }