Add ensure_wallpaper_drawn_on_display_switch flag

Creates a flag for b/395612286 where we will
ensure that we add a show_wallpaper flag during
display switching on foldable devices.

Bug: 395612286
Flag: com.android.window.flags.ensure_wallpaper_drawn_on_display_switch
Test: presubmit
Change-Id: Id40eb7cefb122b211212651d73eac0060c9ec920