Arrange WallpaperTokens by show-when-locked

In cases where we have multiple wallpapers and we need to reorder them
based on keyguard state, there needs to be:

 (1) an api to identify which tokens are supposed to show-when-locked
 (2) a way of moving the tokens around without removing/remaking them

Bug: 268136910
Change-Id: Ib3b0fe97679d5d6ee8281932041e8d0b72af5ef9