Support Twemoji-unsupported ZWJ emoji in Firefox

[nolanlawson]

(Follow-up to #453.)

Firefox is no longer showing "double" emoji, but now it is permanently hiding them, even on OSes where the built-in font (Noto, Apple, Segoe) supports them. E.g. "head shaking horizontally" (🙂‍↔️), "head shaking vertically" (🙂‍↕️), and "phoenix" (🐦‍🔥) are removed from the picker:

This is better than rendering double emoji, but it's sub-optimal because we could just use the OS font if it has better support:

There is a bug on Firefox from 2023 about how their in-browser Twemoji font is out of date (14.1 only, no 15.0 or 15.1).

A few options:

• Remove Mozilla Twemoji entirely from the font list
• Reorder it to give preference to fonts that are likely to be more up-to-date (e.g. Noto and Apple, Segoe is more dicey due to Windows 10)
• Figure out a way to give preference to ZWJ characters to fonts that don't render it as a double character

Current fonts:

https://github.com/nolanlawson/emoji-picker-element/blob/e25c69b95e206ff9d207e727d32ff4efb21ba32b/src/picker/constants.js#L31-L32

[nolanlawson]

Another issue with the current approach is that Firefox shows mixed fonts; e.g. in the first screenshot above, "shaking face" (🫨) is rendering with Noto Color since it comes from Unicode 15.0 whereas "face in clouds" (😶‍🌫️) renders in Twemoji since it comes from 13.1.