Add shortcut to install an app to Private space

Introduce long-press shortcut to install a copy
of the main user app to private space.

Test: manual, installed apps in different stores
and tried shortcut
https://screenshot.googleplex.com/6oAVamTytiYmvPC.png
Bug: 316118005
Flag: ACONFIG com.android.launcher3.Flags.enable_private_space_install_shortcut DEVELOPMENT

Change-Id: I702cd2a27388e3cc6e9e126308d5479836ba6655