Always reorder surfaces on focus change

If the focus change, the surfaces must always be re-ordered, or the
divider ends up behind the focused task, which prevents inputs from
reacing it.

Fix: 377960322
Test: atest DesktopTilingWindowDecorationTest
Flag: com.android.window.flags.enable_tile_resizing
Change-Id: I6c3bd961eb673c1b94038dcfe652539df2af1f48