feat(android.NearbyTransitPage): leave / rejoin vehicles channel after backgrounding #2835

Job	Run time
Run pre-commit to check formatting and linting	2m 19s
Run Android instrumented tests in emulator (28, default, x86)	8m 33s
Test for Android	2m 18s
Build for Android	8m 7s
Upload to Google Play	0s
	21m 17s

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