Hide pointer icon while navbar is hidden

When the navbar gets hidden as a result of
View.setSystemUIVisibility call, the most recent pointer gets
stuck because hover events stop being dispatched to the app.
Hide the pointer icon to avoid confusion.

Bug: 32248070
Test: ApiDemos > View > System UI Visibility > System UI Modes >
   click on HIDE_NAV

Change-Id: Iae80bfa7ab5469946485a68e5308ea752a4645b0