[DO NOT MERGE] Sort A11yService#getWindows by layer descending

This is what A11yService#getWindows promises in the javadoc.

Fixes: 71581072
Test: using testback ensure the order is correct
Change-Id: I5038c4de29c60e235b65751f7bd7771ef35eb339
(cherry picked from commit f40da1a884493b6af61e3b978fdf7c7ff059b2dc)
4 files changed