Convert "Time Zone" field from freeform text into TZ database time auto-completion / suggestions

[jwflory]

Tested on 4.0.0-beta.11.

Summary

When adding a Time Zone to a Proton Contact, auto-complete / offer suggestions of TZ database time and check the user selected a valid TZ database time.

Background

Specifying a time zone is useful for me, and could be used for exciting future mail features like seeing what local time it is for a Proton Contact when sending them an email. However…

For now, it would help to standardize and validate user input for the Time Zone field. In my contacts, I store time zones as a TZ database time string. However, there are a lot of strings to remember and it would help me enter correct metadata if auto-completion kicked in for continents or city names.

Details

When the user types into the box, show a dropdown with suggestions of TZ database time strings. The user should also be able to click on an arrow to show a list of database times so the feature is more obviously exposed for a first-time user.

Outcome

Consistent and standardized data stored between Proton Contacts for Time Zone