Ensure matching insets for taskbar gesture and 3 button nav

* WM checks that the number of insets don't change for
a given window once it's added. Previously when we changed
nav modes the window was removed and a new one was added, so
changing insets amounts/types didn't matter.
* Now that we use the same window and re-provide the insets,
the number of them provided have to match (insets values themselves
can change as much as needed)
* Fix minor bug when checking bit mask for gravity

Test: Switch between nav modes, no crash; no change in behavior
w/ flag turned off
Bug: 274517647
Flag: persist.wm.debug.hide_navbar_window
Change-Id: I750f843e8210ba1c800b61ac79664265924c054a

Change-Id: Idba4e8e1888fa58bf872c04cb042f77a8b5b0573