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.
---
- [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.
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/22871)
<!-- Reviewable:end -->
