Auto merge of #27373 - asajeffrey:webxr-clear-every-frame, r=Manishearth

Updated webxr

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Updates webxr to clear the render target every frame.

---
<!-- 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 #27286 (really this time)
- [x] These changes do not require tests because we don't reftest webxr

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Cargo.lock

@@ -6825,7 +6825,7 @@ dependencies = [
 [[package]]
 name = "webxr"
 version = "0.0.1"
-source = "git+https://github.com/servo/webxr#b170a86c081f762d201d3e870febc6e900ad365b"
+source = "git+https://github.com/servo/webxr#2ff286efcf8bc85fbe2fc91df1aefb1aff911781"
 dependencies = [
  "android_injected_glue",
  "bindgen",
@@ -6848,7 +6848,7 @@ dependencies = [
 [[package]]
 name = "webxr-api"
 version = "0.0.1"
-source = "git+https://github.com/servo/webxr#b170a86c081f762d201d3e870febc6e900ad365b"
+source = "git+https://github.com/servo/webxr#2ff286efcf8bc85fbe2fc91df1aefb1aff911781"
 dependencies = [
  "euclid",
  "ipc-channel",