Improve WebXR layers feature testing (mrdoob#30112)

Author: toji

examples/webxr_vr_layers.html

@@ -305,15 +305,17 @@
 				const gl = renderer.getContext();
 
 				// Init layers once in immersive mode and video is ready.
-				if ( session && session.renderState.layers === undefined ) {
+				const useLayers = session.enabledFeatures !== undefined && session.enabledFeatures.includes('layers');
+
+				if ( session && ! useLayers ) {
 
 					errorMesh.visible = true;
 
 				}
 
 				if (
 					session &&
-					session.renderState.layers !== undefined &&
+					useLayers &&
 					session.hasMediaLayer === undefined &&
 					video.readyState >= 2
 				) {

src/renderers/webxr/WebXRManager.js

@@ -275,7 +275,9 @@ class WebXRManager extends EventDispatcher {
 				currentPixelRatio = renderer.getPixelRatio();
 				renderer.getSize( currentSize );
 
-				if ( session.renderState.layers === undefined ) {
+				const useLayers = session.enabledFeatures !== undefined && session.enabledFeatures.includes( 'layers' );
+
+				if ( ! useLayers ) {
 
 					const layerInit = {
 						antialias: attributes.antialias,