Allow tasks to specify behavior on parent removal.

Adds mReparentOnParentRemoval to determine whether a Task will reparent to another display area when its parent is removed. This value can be specified when creating a root task.

Bug: 391652399
Test: Manual; disconnect displays containing task with flag set.
Flag: com.android.window.flags.enable_display_disconnect_interaction
Change-Id: I1a27776d519d8930f1412497afc19eab54edc29c