Remove special logic for top/bottom gesture insets

With the removal, only the insets with mandatory gesture types provides
mandatory gesture insets. Previously we treat the top and bottom gesture
insets differently.

Modified to addWindowLw to let the bars provide correct insets type
corresponding to the change.

Bug: 161689946
Test: DisplayPolicyTests DisplayPolicyLayoutTests
Change-Id: I91f19d4b50d06a8afcac8355d08e1634973127f1