Shut down Servo when the ML app quits
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Shut down servo when shutting down the magic leap app.
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Reduce the amount of EGL buffer swapping the ML port is doing
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At the moment, we're swapping the EGL buffers every heartbeat, which produces a lot of flickering. We should only swap the buffers when needed.
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<!-- 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 do not require tests because we have no way to test on ML
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This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/22044)
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