A11Y - User switcher - Don't focus on Cancel button

Attempt #2

It is the only item initially visible in the layout, and gets
focus and read by talkback. Initially hide all elements until
they views are bound, then set the visibility.

Fixes: 436691870
Test: talkback - launch from user switcher widget
Flag: EXEMPT bugfix
Change-Id: I1d4690bd05ecd832547234d5c586d3b8130bf42d