Add variation selectors to symbols that exist in both sym and emoji

[MDLC01]

This PR fixes #21, fixes #23, and closes #25, by adding the appropriate variation selectors to symbols that exist in both sym and emoji. I verified that all the variation sequences are defined in by Unicode.¹²

I have marked this PR as a draft because the next step is to add variation selectors to all symbols that allow it, whether present in both sym and emoji or not, to prevent ambiguity.

This made me realize that some emojis are poorly named, but improving this is a task for a separate PR.

Related: typst/typst#6489 (comment).

Footnotes

1. https://www.unicode.org/reports/tr51/#Emoji_Variation_Sequences ↩

2. https://www.unicode.org/Public/UCD/latest/ucd/emoji/emoji-variation-sequences.txt ↩

[Enivex]

This made me realize that some emojis are poorly named,

It's a lot of them. My recentish pr only covered a small part.

[T0mstone]

I'll be the first to bring up automation here:
Whether we want to automate this in the future or not, I think we should definitely have all of these hard-coded in the source code, since such automation would probably take a lot of time that we shouldn't have to pay on each build.
The automation would then only be an optional verification step like in #9. (And maybe we always enable it in CI)

That means any concerns about such automation should not block this PR.