Multi scenario screenshot test

[richardTingle]

As discussed at https://hub.jmonkeyengine.org/t/screenshottests-use-a-image-from-a-different-test-as-reference/49395/4 adds a mechanism to test multiple (theoretically identical) scenarios against a single set of reference images. Example usage:

public class MultiTest extends ScreenshotTestBase {

    @Test
    public void multiTest() {
        
        screenshotMultiScenarioTest(
                new Scenario(
                        "setByParts",
                        new BaseAppState() {
                            @Override
                            protected void initialize(Application app) {
                                Box box = new Box(1, 1, 1);
                                Geometry geom = new Geometry("Box", box);
                                Material mat = new Material(app.getAssetManager(), "Common/MatDefs/Misc/Unshaded.j3md");
                                mat.setColor("Color", ColorRGBA.Blue);
                                geom.setMaterial(mat);

                                geom.setLocalTranslation(1, 0, 0);

                                ((SimpleApplication) app).getRootNode().attachChild(geom);
                            }

                            @Override
                            protected void cleanup(Application app) {}

                            @Override
                            protected void onEnable() {}

                            @Override
                            protected void onDisable() {}
                        }),
                new Scenario(
                        "setByVector",
                        new BaseAppState() {
                            @Override
                            protected void initialize(Application app) {
                                Box box = new Box(1, 1, 1);
                                Geometry geom = new Geometry("Box", box);
                                Material mat = new Material(app.getAssetManager(), "Common/MatDefs/Misc/Unshaded.j3md");
                                mat.setColor("Color", ColorRGBA.Blue);
                                geom.setMaterial(mat);

                                geom.setLocalTranslation(new Vector3f(1f, 0, 0));

                                ((SimpleApplication) app).getRootNode().attachChild(geom);
                            }

                            @Override
                            protected void cleanup(Application app) {}

                            @Override
                            protected void onEnable() {}

                            @Override
                            protected void onDisable() {}
                        })
        ).run();
    }
}

It will test that:

• Every scenario generates the same screenshot(s)
• The first scenario has the same screenshot(s) as the reference image(s)