DesktopCtr/SplitScreenCtr: Supply dispId when starting New Window Split.

When starting new window => splitscreen via calling splitscreen
controller, even if a launchDisplayId is supplied in ActivityOptions,
since Splitscreen's RootTask is always on the default display, Core will
not be able to start splitscreen on non-default display as its parent is
still on the original display.

Pass the displayId, and StageCoordinator will then reparent the Root
Task to the new display.

Bug: 415268190
Test: atest
Flag:com.android.window.flags.enable_non_default_display_split
Change-Id: Ie1d0498067c9e984968031772047da8bc29fbd52