tests: Add avm2/focus_stage test

This test verifies the behavior of focus and focus highlight
for the stage object.

tests/tests/swfs/avm2/focus_stage/Test.as

@@ -0,0 +1,26 @@
+package {
+
+import flash.display.Sprite;
+import flash.text.TextField;
+import flash.display.Sprite;
+import flash.display.Shape;
+import flash.display.MovieClip;
+import flash.events.FocusEvent;
+
+[SWF(width="50", height="50", backgroundColor="#000000")]
+public class Test extends MovieClip {
+    public function Test() {
+        super();
+
+        var shape = new Shape();
+        shape.graphics.beginFill(0xFFFF0000);
+        shape.graphics.drawRect(10, 10, 30, 30);
+        shape.graphics.endFill();
+        this.stage.addChild(shape);
+        this.stage.addEventListener("focusIn", function (evt:FocusEvent):void {
+            trace("Focus changed to stage");
+        });
+        this.stage.focus = this.stage;
+    }
+}
+}

tests/tests/swfs/avm2/focus_stage/output.txt

@@ -0,0 +1 @@
+Focus changed to stage

tests/tests/swfs/avm2/focus_stage/test.toml

@@ -0,0 +1,6 @@
+num_ticks = 1
+
+image_comparisons."output".trigger = 1
+
+[player_options]
+with_renderer = { optional = false, sample_count = 1 }