Make widget pickers edit text box parent focusable.

This is so that when focus is cleared from edit text box, the focus
fallbacks to parent view when external keyboard is used.

Bug: b/197129170
Test: Manually checked that behavior is okay when widget picker and
search is used with and without keyboard. Manually checked talkback
navigation is ok.

Change-Id: Iec2e1ff183dae20803ba2f6eb6e260d2a57779b8