Update DisplayContext for SplitWindowManager when needed.

When we get a new display configuration, we need to also update the mContext object on SplitWindowManager in order for all the views inflation on the next cycle to be done correctly.

Bug: 438264865
Test: Manual - Splitscreen on external display now has correct rounded corners
Flag: com.android.window.flags.enable_non_default_display_split
Change-Id: I54cac923d3925501178c6dae274efdb30944bc38