Arrows to scroll recent tasks in KQS

Bug: 397878339
Bug: 397975686
Flag: com.android.launcher3.taskbar_overflow
Test: Enter taskbar overflow, and open the overflow view.
    Verify that arrow buttons are present; tapping them scrolls in the
    correct direction; when fully scrolled in a direction, the
    associated arrow button is disabled; verify arrow buttons have hover
    effects.
    Open Alt+Tab view, verify no buttons are present if the view cannot
    be scrolled (and present if the view can be scrolled).

Change-Id: Id1c37a2967a629aeb4b3cc2dc5ff7efb21c90cbe