feat(bevy_xr_utils): add GenericTracker component and implement XR_MNDX_xdev_space as a backend

Signed-off-by: Schmarni <marnistromer@gmail.com>

crates/bevy_xr_utils/examples/mndx_xdev_spaces.rs

@@ -0,0 +1,67 @@
+use bevy::prelude::*;
+use bevy_mod_openxr::{add_xr_plugins, exts::OxrExtensions, init::OxrInitPlugin, resources::OxrSessionConfig};
+use bevy_mod_xr::hand_debug_gizmos::HandGizmosPlugin;
+use bevy_xr_utils::{
+    generic_tracker::GenericTrackerGizmoPlugin, mndx_xdev_spaces_trackers::MonadoXDevSpacesPlugin,
+};
+use openxr::EnvironmentBlendMode;
+fn main() -> AppExit {
+    App::new()
+        .add_plugins(add_xr_plugins(DefaultPlugins).set(OxrInitPlugin {
+            exts: {
+                let mut exts = OxrExtensions::default();
+                exts.enable_hand_tracking();
+                exts.other.push("XR_MNDX_xdev_space".to_string());
+                exts
+            },
+            ..Default::default()
+        }))
+        .insert_resource(OxrSessionConfig {
+            blend_mode_preference: vec![
+                EnvironmentBlendMode::ALPHA_BLEND,
+                EnvironmentBlendMode::ADDITIVE,
+                EnvironmentBlendMode::OPAQUE,
+            ],
+            ..default()
+        })
+        .insert_resource(ClearColor(Color::NONE))
+        .add_plugins((
+            HandGizmosPlugin,
+            GenericTrackerGizmoPlugin,
+            MonadoXDevSpacesPlugin,
+        ))
+        .add_systems(Startup, setup)
+        .run()
+}
+
+/// set up a simple 3D scene
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    // circular base
+    commands.spawn((
+        Mesh3d(meshes.add(Circle::new(4.0))),
+        MeshMaterial3d(materials.add(Color::WHITE)),
+        Transform::from_rotation(Quat::from_rotation_x(-std::f32::consts::FRAC_PI_2)),
+    ));
+    // cube
+    commands.spawn((
+        Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 1.0))),
+        MeshMaterial3d(materials.add(Color::srgb_u8(124, 144, 255))),
+        Transform::from_xyz(0.0, 0.5, 0.0),
+    ));
+    // light
+    commands.spawn((
+        PointLight {
+            shadows_enabled: true,
+            ..default()
+        },
+        Transform::from_xyz(4.0, 8.0, 4.0),
+    ));
+    commands.spawn((
+        Camera3d::default(),
+        Transform::from_xyz(-2.5, 4.5, 9.0).looking_at(Vec3::ZERO, Vec3::Y),
+    ));
+}