Use a test VRDisplay that renders to a GL window
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Add a `dom.webvr.test` pref that registers a new VR display, which registers to a GL window.
The matching webvr PR is https://github.com/servo/rust-webvr/pull/66.
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#22795
- [X] These changes do not require tests because we need a followup PR to support reftests which use the VR display
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Use simpleservo embedding API for Magic Leap
This removes the duplication between the two ports and makes it easier to improve all of our embeddings simultaneously.
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#22065
- [x] These changes do not require tests because no automated tests for embedded devices.
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Support for ExternalVR implementation
This PR adds the hook necessary for the ExternalVR rust-webvr driver.
Waiting on rust-webvr 0.9.3 to be published before landing.
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