Mitigate the problem of moving the current block down sets the caret to the wrong block

[daniloercoli]

This PR does help on mitigating the problem reported in #311, where under some circumstances the caret is moved to another block when the current TextInput powered block in moved down by the user. The problem was originally reported for Android, but it seems could happen on iOS too, even though with less frequency.

In this PR we're just hiding the Keyboard on block Up/Down/Delete operations.

A GIF of the original problem

During my tentative to fix the problem I've also found other scenarios where the same issue comes up on writing.
IE:

• Tap on a para block (that's not the first one on the list)
• Tap on the Page break block
• Boom 🤯 the caret is moved to the first TextInput block in the list
  For more details see the comment and video linked here Moving the current block down sets the caret on the wrong block #311 (comment)

To test

• Start the demo app
• Select a RichText block that is not the first in thelist, IE. Hello World block
• Tap the down arrow on the toolbar
• The block is correctly moved down and the keyboard dismissed

[hypest]

LGTM!