Auto merge of #22094 - asajeffrey:magicleap-shutdown, r=paulrouget

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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- [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 don't test ML

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