Fixes un-setting activity type when embed activity in split-screen

An exception was thrown by launching the split-screen from the recent
app. It happens while embedding activities in split-screen. System
reparent the tasks from split-root to displayArea when return to home
screen. The reparent’s action is ignored while dealing with the task
whose activity’s type is TYPE_UNDEFINED. Split-screen shell expects
the task of activityType is TYPE_STANDARD. That’s why the system
throws the legal argument exception because the task is already a
child of the root task.

The CL looks for the top non-finish activity first before the top
child in the task for resolving the task activity type. For example,
when add child into TaskFrag#2, this CL resolve the activity type
from activity#1 of Task#49.

 -- Task#49
    -- TaskFrag#2
       -- activity#2
    -- TaskFrag#1
       -- activity#1

Bug: 228592780
Test: 1.Drag settings from taskbar into split and launch DWB
      2.Return to home and launch the split-screen.

Change-Id: I69960b34c909071ce0cce5ff11c630faf6106f6c