Fix unknown items issue when using Switch Access

Switch access finds the actionable item in parent view,
however, it can't find any readable text so it speaks
unknown item.

To solve this problem, we have to set focusable attribute
as false for child views, so they will be grouped in the
parent view together. Then, Switch Access can recognize
the text info with title and learn more.

Test: Play around the switch access and talkback. Both
can speak correct message in the footer.
Fix: 187241610
Bug: 209528395

Change-Id: I20a8bfa1fe1546170d254deaaff42cd4de180f5c