Allow specifying gravity for overlay display

In the test linked below, the overlay was displayed above the area the test was interacting with. By specifying the gravity, we can move the overlay away from that area.

Test: android.platform.test.scenario.sysui.mediaprojection.MediaProjectionPermissionTest#openPermissionActivity_secondaryDisplay
Bug: 377416832
Flag: EXEMPT Bug fix
Change-Id: If9e150d011fd7b07a23061ef4f6f975b4f5d6601