Use updated orientation for split screen in connected display

In DesktopModeWindowDecorViewModel, the orientation used in moveToSplit
was calculated from outdated context when split screen is started in
connected display. This CL updates the logic to use context from
new display to make sure the orientation represents what's in connected
display.

Bug: 438285797
Test: manual && atest
Flag: EXEMPT BUGFIX
Change-Id: I7dfc9d2725b2aea7dab2ef5d868ace1739fb1a0f