Use Taskbar window for phones (only works on gesture nav) with flag

* Try to avoid re-creating TaskbarActivityContext to
avoid re-inflating taskbar views
* Toggle via Flipper App (key 1101)
OR adb shell setprop persist.wm.debug.hide_navbar_window 1 && adb reboot
TODOs
* Only works for gesture nav, not 3 button
* Sampling on phone doesn't always work.

Bug: 219035565
Change-Id: I2a015f99d5f1fe86d7261eec9fd898bd4480ff9f