* Disable Video block on Android for v1.7.0 release

* Add import statement to check platform

* Remove focus from RichText when unmounting

In #15999 this behavior was changed to prevent the keyboard from disappearing
when you press Enter to create a new paragraph.

This worked in that case, but had the side effect of TextInputState still
thinking a dead view had focus, and causing a crash in some scenarios.

* Only blur a RichText in replaceable block

That RichText won't have the chance to blur earlier so, we need to do it
on unmount. But, non replaceable blocks wont need to blur their RichText
on unmount because that will happen normally in componentDidUpdate().

* Rename to an unstable, very goal-named name

* Compute shouldBlurOnUnmount inside RichText