Pin footer actions to bottom of QSContainerImpl

These pins the actions and decouples the FooterAction controller from
Footer controller. Pinning the actions is behind a flag, because the UI
is not finalized.

Fixes: 216302612
Test: atest com.android.systemui.qs com.android.systemui.statusbar.phone
Test: manual in different screen sizes

Change-Id: I0cd24596d0b900b2555202f59047ebad5c969afb