[2.x] Emoji: Update to Emoji/Unicode 17

[dsevillamartin]

Changes proposed in this pull request:

• Update to Emoji/Unicode 17 for new emojis (from 14)
• Replace twemoji package with @twemoji/api
• Add migration to delete CDN if it starts with old jsdelivr

Reviewers should focus on:
I don't love the CDN url being set by default in the backend, as a user can go in and modify it and save such that it may be equal to the default, but now has a value in their DB and so it's technically a custom CDN. Though this shouldn't come up very often. I'd rather have it as a constant in the common JS and pass that when missing a setting (and to the locale -- should not be in the translation text imo).

Also, regarding CDN: For fof/reactions (see FriendsOfFlarum/reactions@d0d60a6), I used Emoji/Unicode 16 since the CDN we use (cloudflare's cdnjs) does not have the latest version (see cdnjs/cdnjs#14263). We use jsdelivr as a default here, but it may cause issues with those that use a custom one to avoid geoblocking?

Screenshot

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.