(dev/core#4531) Afform Mail Tokens - Fix rendering for localized/individual email

[totten]

Overview

While sending the localized email, some UF's may reboot the container mid-execution. This change ensures that the listeners will be re-registered.

For steps to reproduce and more analysis, see https://lab.civicrm.org/dev/core/-/issues/4531

ping @larssandergreen

Before

• When you "Send email" to a contact with a preferred_language, the {afform.*} tokens do not render.
• Afform's listeners are registered during the first container boot - but not during a second or third boot (as by Drupal::setUFLocale())

After

• The tokens do render.
• Afform's listeners are consistently re-registered, even if the container starts multiple times.

Comments

This also makes the code prettier.

The bug is technically a regression (circa 5.53/5.54), but it's a bit old. I think 5.65-rc makes sense. (Backporting to 5.64-stable is more debatable. If others want that, then I'd be OK with it.)

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[larssandergreen]

Works for me, looks good, thanks @totten!