Allow video to go complete fullscreen on Android

[zarmhast]

Hide the navbar on Android devices with onscreen navigation.

Fixes #2324

Details about this fullscreen option can be found on Fullscreen API documentation:
https://developer.mozilla.org/en-US/docs/Web/API/FullscreenOptions/navigationUI

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[zarmhast]

@googlebot I signed it!

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[joeyparrish]

Thank you for the contribution!

Unfortunately, the linter will complain about the style in this change. We use single quotes by convention. In the future, please run python build/all.py to run the linter and compiler yourself before submitting a PR.

In this case, the compiler will also complain because it doesn't know about this additional argument to requestFullscreen. It was only added in Chrome 71 about a month ago, and the "externs" the compiler uses to define the built-in APIs in the browser don't have this definition.

The latest version of the compiler has the updated definition, but we are unable to upgrade it right now because of other issues in our codebase. So this will be tricky to solve, and may require some kind of workaround.

Since this compiler is so complicated, I will update your change for you and test it before merging.

Thanks for bringing this to our attention!

[joeyparrish]

Just pushed a workaround for the compiler issue in 51c3717.

[joeyparrish]

I pushed your change manually in 3dc0b17 with style fixes in ee91f4a. I expected github to notice and close the PR, but for some reason, it did not.

Thanks again!

[zarmhast]

@joeyparrish, thank you. Didn't have the dev environment set up, but will do next time. Thank you for your help.

[joeyparrish]

Always happy to help!

[joeyparrish]

This PR has been cherry-picked for v2.5.8.