Add flag to guard wallpaper token transition change

Bug: b/347593088
Flag: com.android.window.flags.ensure_wallpaper_in_transitions
Test: presubmits
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:6cf4a370b32f6d979caacb57375d8c0c434bd4ac)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:c4e56f87214b5cb057f9cf5e61503ff838dacead)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:1a49bad13a37712be110ad8833509ad32d69d69a)
Merged-In: Idda8e20b4362de965f6256cedff829e4bbd8ffb1
Change-Id: Idda8e20b4362de965f6256cedff829e4bbd8ffb1