Optimize updating hotseat items in overflown taskbar

The logic for updating hotseat items in taskbar involved adding all
available recent items to the view, and then removing ones that
overflow. It also preemptively added overflow icon, and then removed it
when no overflow was detected.

This cl updates logic to stop adding recent items before they cause
overflow, and add overflow icon only when needed.

Bug: 368119679
Test: Keep opening apps until taskbar enters overflow, and verify that
expected number of app icons is displayed, and overflow icon is shown in
the correct place.
Flag: com.android.launcher3.taskbar_overflow

Change-Id: Icaad4386b54bbfccba8ace5876d7fe5c90cb7798