Scaffolding for selection & scanning modes

The gizmo currently draws as an annulus with the intention that it is an
area selection tool. These new components will serve as mode selectors
so that different selection modes can be used.

src/debug_plugin.rs

@@ -15,7 +15,7 @@ fn setup(
     mut materials: ResMut<Assets<ColorMaterial>>,
 ) {
     commands.spawn((
-        Cursor,
+        ScannerWidget::default(),
         MaterialMesh2dBundle {
             mesh: meshes.add(Annulus::new(9.5, 10.0)).into(),
             material: materials.add(Color::srgb(0.0, 0.0, 0.0)),
@@ -24,9 +24,38 @@ fn setup(
     ));
 }
 
+#[derive(Bundle)]
+struct ScannerWidget {
+    cursor: Cursor,
+    select: SelectionMode,
+    scan: ScannerMode,
+}
+
+impl Default for ScannerWidget {
+    fn default() -> Self {
+        Self {
+            cursor: Cursor,
+            select: SelectionMode::CircularArea,
+            scan: ScannerMode::CenterOfMass,
+        }
+    }
+}
+
 #[derive(Component)]
 struct Cursor;
 
+#[derive(Component)]
+enum SelectionMode {
+    NearestSingle,
+    CircularArea,
+}
+
+#[derive(Component)]
+enum ScannerMode {
+    CenterOfMass,
+    Velocity,
+}
+
 fn update_cursor(
     window: Query<&Window, With<PrimaryWindow>>,
     camera: Query<(&Camera, &GlobalTransform)>,