Do not dismiss split if stages are not visible due to screen is sleeping

Pass isSleeping information in TaskInfo to determine whether the task is
sleeping due to display state. Prevent to dismiss staged split when
both stages is not visible due to the display is sleeping, like keyguard
showing or screen off.

Bug: 188010345
Test: atest WMShellUnitTests
Test: verified staged split won't be dismissed while keyguard showing
and screen off.

Change-Id: I0ee8943b035a9e9f937c22d2a228913e597ac79f