Required changes identified in our review on T327570:
* [x] Don't try to save preferences for temp users – use cookies or local storage instead where applicable, like for logged out users
** https://gerrit.wikimedia.org/r/c/mediawiki/extensions/MobileFrontend/+/913201
* [x] Update messages about revealing your IP address
** {T335530}
** {T335532}
** https://gerrit.wikimedia.org/r/c/mediawiki/extensions/MobileFrontend/+/913001
* [ ] Correct signature in the preview when a temp user would be created
* [x] {T332437}
** https://gerrit.wikimedia.org/r/c/schemas/event/secondary/+/907960
** https://gerrit.wikimedia.org/r/c/mediawiki/extensions/WikimediaEvents/+/907964
And identified in Tim's initial review on T307054:
* [x] In the mobile editor, saving as an anonymous user should create the temporary account…
** https://gerrit.wikimedia.org/r/c/mediawiki/core/+/837131
* [ ] …and redirect through login.wikimedia.org in order to acquire CentralAuth cookies.
* [ ] Then (maybe) show a post-save notification as in core.