Summary:
ScrollView has special behavior when the keyboard is open, but starts listening to keyboard events on mount. This means a ScrollView mounted after the keyboard is already up (e.g. for a typeahead) is not initialized to the keyboard being up.
This change adds `Keyboard.isVisible()` and `Keyboard.metrics()` APIs to allow seeding initial keyboard metrics.
Changelog:
[General][Fixed] - Inform ScrollView of Keyboard Events Before Mount
Reviewed By: JoshuaGross, yungsters
Differential Revision: D38701976
fbshipit-source-id: 42b354718fbf5001ca4b90de0442eeab0be91e7a