Tapping overflow button toggles KQS

Updates the taskbar overflow button handler to toggle the KQS instead of
merely showing it. The toggle action will open KQS view if it's not
visible, or close it if it's visible and has been shown from the
taskbar. If the view is shown, but in response to Alt+Tab, the view will
be closed, and reshown above the task bar.

Requires CL:30016166 for tapping to work as expected, and CL:30074037
for tapping overflow button reopen KQS over shelf if KQS is already
active for Alt+Tab

Bug: 368119679
Test: Enter task bar overflow. Tap overflow button to show KQS, tap
overlow button to hide KQS. Press Alt+Tab, tap overflow button to
reshow KQS over taskbar, and with filtered set of tasks.
Flag: com.android.launcher3.taskbar_overflow

Change-Id: Id598f9cad649aa174aaf1c5802bf6b6837413d1e