Use correct gravity for 3-button gesture insets

3-button nav bar can be on sides instead of the bottom when the display
rotates, always use the nav bar height value from the resource and put
it at the bottom as mandatory gesture insets is not a reliable way to
provide the correct value. Use the nav bar frame for the insets.

Bug: 273445780
Test: TaplTestsLauncher3
Test: See reproduce steps in the bug
Change-Id: I19e87390dbf7ade1e5b2fb6490f8ca550c476026