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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