chore: switch formatter to format-message

[SychO9]

Fixes #3702
Fixes #3734
Fixes #3685
Closes #3735

Changes proposed in this pull request:

• Switches to the more mature format-message package instead of the less capable one we currently use.

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

[SychO9]

forum side: +3.11KB
admin side: +2.85KB