Add item reselected listener to BottomNavigationView

Adds an additional listener in for developers that want to discern
between item selection and reselection without tracking the current
selection. This maintains backward compatibility with existing uses
of OnNavigationItemSelectedListener by itself in client code; new
behavior is only observed if an OnNavigationItemReselectedListener is
added.

Bug: 34576220
Test: Modified tests in BottomNavigationViewTest,
      Updated support-design-demos

Change-Id: Id48cde6395dd73a01ce68e3be1783161229f8939
4 files changed