Inherit source task windowing mode if available

Transfers the launch windowing mode from the source task if available
to the launching task. This closes a gap in proto2's windowing mode
launch calculation in Shell (DesktopTasksController#handleRequest)
where task trampolines are one single transition, so an old task that's
relaunched by a new task is never a "trigger task" in #handleRequest
and its windowing mode can't be adjusted by Shell based on the current
desktop mode shell state.

This change still relies on the windowing mode being set by
handleRequest on the trigger task, which is then transfered to the task
that is launched by the trigger task.

Bug: 286929122
Test: manual:
 (1) Launch Calendar in fullscreen, launch Chrome in fullscreen, drag
Chrome into desktop mode, launch Calendar from taskbar - verify it
launches in freeform mode.
 (2) Launch Calendar in fullscreen, launch Chrome in fullscreen, drag
Chrome in to desktop mode, swipe up to go Home, launch Calendar from
Home - verify it launches in freeform mode.
 (3) Launch Calendar and enter desktop mode, launch Chrome in freeform,
drag Chrome to top to exit desktop mode, launch Calendar from taskbar -
verify it launches in fullscreen.
 (4) Launch Calendar and enter desktop mode, launch Chrome in freeform,
drag Chrome to top to exit desktop mode, swipe up to go Home, launch
Calendar from Home - verify it launches in fullscreen mode.

Change-Id: I27f50e661c155b6e504b49fc044b889135af7b09