Tapping overview button when quickstep enabled shows overview

This is the systemui side of showing launcher's overview when it decides
to allow users to trigger overview with the overview button in the
navigation bar when quickstep is enabled.

Test: manual - tap overview button in nav bar
Bug: 67957962
Change-Id: I0d59d60d4b4ce1df9dcf2a745f9a5efd415b8582