DO NOT MERGE Only set the LAYOUT flags if the window is fullscreen

This addresses an issue where toasts will be hidden due to the setting
of the LAYOUT_HIDE_NAVIGATION flag.

Bug: 148180738
Test: manual (adb shell settings put global policy_control "immersive.navigation=*" then try to show a toast with gravity top)
Change-Id: Ic47edc5423c4daf373fc3a8bfc30af15cadd6d90