Reparent split root for split select in external display

When split select is initiated on external display, the split pair should be started on external display. This CL reparents the current split root task to the correct display by checking the current task displayId.

Test: manual
Bug: 432271801
Flag: com.android.window.flags.enable_non_default_display_split_bugfix
Change-Id: I7e98c9300b2f30305998f09c25d379efbbb24d50