Add PopupMenu#setForceShowIcon

The API enables developers to display icons for menu items. Before this,
the common workaround was to reflect in MenuPopupHelper (non-public
class), and call setForceShowIcon there.

Bug: 123769396
Test: atest android.widget.cts.PopupMenuTest
Change-Id: If4ef46bc7786a2e7e756a9b15c81147e0cce1090