Implement Install Apps button in Private Space.

UX mock: https://www.figma.com/file/K6bIIcG882EiJNjxvSWsFT/V%E2%80%A2-Private-Space?node-id=7246%3A83750&mode=dev
UX icon spec: https://www.figma.com/file/K6bIIcG882EiJNjxvSWsFT/V%E2%80%A2-Private-Space?type=design&node-id=19979-224329&mode=design&t=50SDFdomAtonNU4V-0

Video: https://drive.google.com/file/d/1VtTzxR46dLiaozOo6sOHADv1qTcBOwDP/view?usp=sharing
Screenshot:
https://screenshot.googleplex.com/3ShcUozVrkGMHbc
https://screenshot.googleplex.com/3F4c3yzJ7RUpma7

Reason to use PrivateSpaceInstallAppButtonInfo: reuse `VIEW_TYPE_ICON`, which needs an AppInfo.

Bug: 308064949
Test: manual
Flag: ACONFIG com.android.launcher3.private_space_app_installer_button development
Change-Id: I3fb27fae8324d4b276816b17f9b0a2d9b6f33ed2