GestureNav: Limit exclusion rects

Add limits for system gesture exclusion on the left and right edges.
This prevents non-immersive-sticky apps from totally disabling the
back gesture.

Bug: 135522625
Test: atest SystemGestureExclusionRectsTest

Merged-In: Ib26161663a6aababe803d3c70044f4017bdbe675
Change-Id: Ib26161663a6aababe803d3c70044f4017bdbe675

• api/test-current.txt[diff]
• core/java/android/provider/DeviceConfig.java[diff]
• services/core/java/com/android/server/wm/DisplayContent.java[diff]
• services/core/java/com/android/server/wm/WindowManagerService.java[diff]
• services/core/java/com/android/server/wm/utils/RegionUtils.java[diff]
• services/tests/wmtests/AndroidManifest.xml[diff]