Fix bug with double-relayout of Overview Actions View

This CL refactors Overview Actions View so that a separate view, R.id.group_action_buttons, is used for buttons related to grouped tasks. This also changes the way visibility is handled with actions buttons -- instead of all buttons living on one bar and being toggled on and off, sometimes the whole bar is toggled on and off (to change from single task actions to group actions and vice versa).

This prevents the same view from having its visibility changed twice in in one layout and causing the wrong visibility to be rendered.

Fixes: 333844287
Test: Manual
Flag: ACONFIG com.android.wm.shell.enable_app_pairs NEXTFOOD
Change-Id: I1b6be4637ac8c8d424e7633c437fca376ecdd757
Merged-In: I1b6be4637ac8c8d424e7633c437fca376ecdd757