Prevent Save App Pair from showing up on 3p launcher

This CL adds a check so that app pairs can't be saved on 3p launchers. This affects the Overview icon dropdown menu and the Overview Actions Bar.

Fixes: 326155701
Flag: ACONFIG com.android.wm.shell.enable_app_pairs TRUNKFOOD
Test: Manual, option does not show up when Nova Launcher is set as default home app, and shows up again for Pixel Launcher.
Change-Id: I60d6fd3b3eb39921edafb12faace743d16de270f