Auto merge of #27499 - asajeffrey:webxr-xrmedia-dummy, r=Manishearth

Add dummy implementations of missing XR layer types

<!-- Please describe your changes on the following line: -->

Add dummy implementations of the missing layer types, and the functions that create them.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -14719,7 +14719,7 @@
      ]
     ],
     "layers.html": [
-     "f64cc1f30f469351b83cd1c12a0584b1db5317a7",
+     "b6749f208a8f3c5ae78fbe72cfa7364829abb127",
      [
       null,
       {}

tests/wpt/mozilla/tests/webxr/layers.html

@@ -48,6 +48,27 @@
               () => { session.updateRenderState({ layers: [layer], baseLayer: layer }); },
               "Setting both baseLayer and layers should fail"
             );
+
+            assert_throws_dom(
+              "NotSupportedError",
+              () => { glLayerFactory.createQuadLayer("texture"); },
+              "Creating a quad layer without the layers feature should fail"
+            );
+            assert_throws_dom(
+              "NotSupportedError",
+              () => { glLayerFactory.createCylinderLayer("texture"); },
+              "Creating a cylinder layer without the layers feature should fail"
+            );
+            assert_throws_dom(
+              "NotSupportedError",
+              () => { glLayerFactory.createEquirectLayer("texture"); },
+              "Creating a equirect layer without the layers feature should fail"
+            );
+            assert_throws_dom(
+              "NotSupportedError",
+              () => { glLayerFactory.createCubeLayer(); },
+              "Creating a cube layer without the layers feature should fail"
+            );
           });
         </script>
     </body>