added tracker markers and change detection

src/xr_input/trackers.rs

@@ -0,0 +1,18 @@
+use bevy::prelude::Component;
+
+#[derive(Component)]
+pub struct OpenXRTrackingRoot;
+#[derive(Component)]
+pub struct OpenXRTracker;
+#[derive(Component)]
+pub struct OpenXRLeftEye;
+#[derive(Component)]
+pub struct OpenXRRightEye;
+#[derive(Component)]
+pub struct OpenXRHMD;
+#[derive(Component)]
+pub struct OpenXRLeftController;
+#[derive(Component)]
+pub struct OpenXRRightController;
+#[derive(Component)]
+pub struct OpenXRController;