A11yMenu Layout fixes

Adjusts A11yMenu to use proper vertical spacing between grid items,
and to do a better job at keeping the footer on the screen with larger display sizes.

Notably, on larger display sizes there is still vertical overlap between text & buttons.

Test: Open a11yMenu in portrait & landscape modes to verify the above behavior. Make sure to test with small & large display sizes.
Bug: 361449952
Flag: EXEMPT small internal change, partially involving xml
Change-Id: If2977338c3b1521f85e903f661f33cf6a9917cc6