Accessibility fix for ShellRoot

Ensure ShellRoot layers are ordered correctly with other windows in the
system. This means placing the Shell Root layers z ordered based on the
window type

Bug: 177864415
Test: adb shell dumpsys accessibility
Change-Id: Iee982e9f17b496d413d4733f0a99997f81cee527
Merged-In: Iee982e9f17b496d413d4733f0a99997f81cee527