pin-shortcut: Implements the actual pinning functionality

This cl implements the onClick function for the pin shortcut, so
that clicking on it will actually pin an app/item to the taskbar.

Bug: 375648361
Test: Manual, Recording uploaded to buganizer
Flag: com.android.launcher3.enable_pinning_app_with_context_menu
Change-Id: Ia0e9464ceb99efd47a9fefd8136b930f908599cb