Use resolved windowing mode to match launch root

WM core offers WindowContainerTransaction#setLaunchRoot() API to
override launch root task for specific windowing modes and activity
types. However before this CL we only pass windowing mode in
ActivityOptions when selecting root task, which will make windowing mode
most of the time unspecified, which diminishes the use of the API.

This can help whoever needs to differentiate launch root for freeform
tasks and fullscreen tasks.

Bug: 182514695
Test: WCT#setLaunchRoot() takes effect with app launches with specific
windowing mode that is initiated by launcher.
Test: atest TaskDisplayAreaTests

Change-Id: I8113d3c9a82c8202f3881b5c08347fcb765861c6