Add a dummy implementation of all the XR Layer types

components/script/dom/xrprojectionlayer.rs

@@ -0,0 +1,11 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use crate::dom::xrcompositionlayer::XRCompositionLayer;
+use dom_struct::dom_struct;
+
+#[dom_struct]
+pub struct XRProjectionLayer {
+    composition_layer: XRCompositionLayer,
+}