SystemUI: Implement hide gestural navigation hint bar

Author: Jesse Chan <jc@lineageos.org>
Date:   Tue Jun 2 13:59:52 2020 +0800

    SystemUI: Set no hint overlay to highest priority

    As overlays are also used to apply navigation mode, it is needed to set
    our customization overlay to highest priority to ensure it is applied.

    Change-Id: I41ca4b7ea99fea9f62d2e8ece5114f682e8e7fe9
    Signed-off-by: Jesse Chan <jc@lineageos.org>

Change-Id: Ic6695dfe929db443f169d59f153e14a6de249590
Signed-off-by: Jesse Chan <jc@lineageos.org>