Allow to send user leave hint for task switch by touch

A corner case if the window on a launching activity is not shown
in-time, a touch event may send to the current top window which
belongs to previous app. That causes task reorder and pauses
the launching activity.

Just to fit the description in document "activity is about to
go into the background as the result of user choice".

Bug: 245423495
Test: Launch a dialog style activity from launcher with
      sleeping(500) in onCreate. And keep clicking launcher
      at the same time. The activity should receive onUserLeaveHint.
Change-Id: Ia7257fe2383bf2a1f55c26170ca047a4604ebd60