tests: Add test for GetVariable/SetVariable on _x, etc.

core/tests/regression_tests.rs

@@ -218,6 +218,7 @@ swf_tests! {
     (color_transform, "avm1/color_transform", 1),
     (with, "avm1/with", 1),
     (prototype_properties, "avm1/prototype_properties", 1),
+    (stage_object_properties_get_var, "avm1/stage_object_properties_get_var", 1),
 }
 
 // TODO: These tests have some inaccuracies currently, so we use approx_eq to test that numeric values are close enough.

core/tests/swfs/avm1/stage_object_properties_get_var/output.txt

@@ -0,0 +1,5 @@
+// get('_x')
+0
+// set('_x', 100)
+// _x
+100