Auto merge of #27487 - asajeffrey:webxr-update-webidl, r=Manishearth,jdm

WebXR Layers update WebIDL

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

Updates the WebXR Layers WebIDL. Implements the "update the pending layers state" algorithm from the layer spec.

---
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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 updated tests for these changes

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -13959,7 +13959,7 @@
      ]
     ],
     "interfaces.html": [
-     "d988b7939f83cef16a51a4ae5502ed029f31df99",
+     "b58b16ca333f9e00afade02c2ac60689ee7eef3a",
      [
       null,
       {}
@@ -14719,7 +14719,7 @@
      ]
     ],
     "layers.html": [
-     "49821d7661f92bc9cf22232d3fcb391c2cdc7295",
+     "f64cc1f30f469351b83cd1c12a0584b1db5317a7",
      [
       null,
       {}