Convert datetime coffeescript spec to ES6

What does this MR do?

Converts the last remnant coffeescript file to ES6

Are there points in the code the reviewer needs to double check?

None

Why was this MR needed?

Because we aren't using coffeescript anymore 🎈

What are the relevant issue numbers?

#21472 (closed)

Screenshots (if relevant)

None

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Tests
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together