Auto merge of #25738 - jsjoeio:jsjoeio/issue-25732-rename-xr, r=Manishearth,jdm

refactor: rename XR to XRSystem

<!-- Please describe your changes on the following line: -->
This PR renames XR to XRSystem.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [X] These changes fix #25732

<!-- Either: -->
- [ ] There are tests for these changes OR
- [X] These changes do not require tests because it's the changing of a name (XR -> XRSystem)

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tests/wpt/metadata/webxr/idlharness.https.window.js.ini

@@ -131,27 +131,9 @@
   [XRSystem interface: operation isSessionSupported(XRSessionMode)]
     expected: FAIL
 
-  [XRSystem interface: existence and properties of interface prototype object]
-    expected: FAIL
-
-  [XRSystem interface: existence and properties of interface object]
-    expected: FAIL
-
-  [XRSystem interface object name]
-    expected: FAIL
-
   [XRSystem interface: attribute ondevicechange]
     expected: FAIL
 
-  [XRSystem interface: existence and properties of interface prototype object's @@unscopables property]
-    expected: FAIL
-
-  [XRSystem interface: existence and properties of interface prototype object's "constructor" property]
-    expected: FAIL
-
-  [XRSystem interface object length]
-    expected: FAIL
-
   [XRSystem interface: operation requestSession(XRSessionMode, XRSessionInit)]
     expected: FAIL
 

tests/wpt/mozilla/meta/MANIFEST.json

@@ -13863,7 +13863,7 @@
      ]
     ],
     "interfaces.html": [
-     "bb6adbde0b3452e6ea8f1db44941a08dbe236774",
+     "163ab416b1627e07347b83aa210712364182343a",
      [
       null,
       {}

tests/wpt/mozilla/tests/mozilla/interfaces.html

@@ -263,7 +263,6 @@ test_interfaces([
   "XMLHttpRequestEventTarget",
   "XMLHttpRequestUpload",
   "XMLSerializer",
-  "XR",
   "XRFrame",
   "XRInputSource",
   "XRInputSourceArray",
@@ -275,6 +274,7 @@ test_interfaces([
   "XRSession",
   "XRSessionEvent",
   "XRSpace",
+  "XRSystem",
   "XRView",
   "XRViewerPose",
   "XRViewport",