Add intermediate screen for anonymous editors

Show anonedit warning for anonymous users when they try to edit.

Reactivate edit for anonymous users for alpha.

Follow up: I7662c204f906bf214369fdd93f92a4a5d4e4081a

Bug: 59937
Change-Id: I8ec64e0255b93195289ec7a76a6df4ce166f6f8d
Merge "Add intermediate screen for anonymous editors"