Fix ViewportPreview upside-down in 3.x.

(cherry picked from commit 1426df66a8397f3f03aaa541399054f0487fc8a1)

editor/plugins/viewport_preview_editor_plugin.cpp

@@ -38,6 +38,8 @@ void EditorInspectorPluginViewportPreview::parse_begin(Object *p_object) {
 	Viewport *viewport = Object::cast_to<Viewport>(p_object);
 
 	TexturePreview *viewport_preview = memnew(TexturePreview(viewport->get_texture(), false));
+	viewport_preview->get_texture_display()->set_flip_v(true); // flip as ViewportTexture in 3.x is upside-down.
+
 	// Otherwise `viewport_preview`'s `texture_display` doesn't update properly when `viewport`'s size changes.
 	viewport->connect("size_changed", viewport_preview->get_texture_display(), "update");
 	add_custom_control(viewport_preview);