Emoji Variation selectors

[T0mstone]

Some symbols have both a text style and an emoji style. These can be explicitly selected with Variation Selectors 15 and 16 (U+FE0E and U+FE0F), respectively.

Without these, there are currently (as of 35c18a1) the following duplicates between sym and emoji:

• sym.hash, emoji.hash
• sym.ast.basic, emoji.ast
• sym.copyright, emoji.copyright
• sym.trademark, emoji.tm
• sym.trademark.registered, emoji.reg
• sym.excl.{double, quest}, emoji.excl.{double, quest}
• sym.arrow.{l.r, t.b, tl, tr, bl, br, {l, r}.hook, {l, r, t, b}.filled, {t, b}.curve}, emoji.arrow.{l.r, t.b, tl, tr, bl, br, {l, r}.hook, {l, r, t, b}.filled, {t, b}.curve}
• sym.square.filled.big, emoji.square.black
• sym.square.filled.{tiny, small, medium}, emoji.square.black.{tiny, small, medium}
• sym.square.stroked.big, emoji.square.white
• sym.square.stroked.{tiny, small, medium}, emoji.square.white.{tiny, small, medium}
• sym.triangle.filled.{l, r}, emoji.triangle.{l, r}
• sym.ballot.check, emoji.ballot.check
• sym.suit.{spade, club, heart, diamond}.filled, emoji.suit.{spade, club, heart, diamond}
• sym.checkmark.heavy, emoji.checkmark.heavy
• sym.dash.wave.double, emoji.dash.wave.double

I haven't looked into which of the styles is the default for each of them, but we should probably give variation selectors to both sides to avoid ambiguity.

Prior work: #21, #23.

[MDLC01]

Note that this is currently blocked by Typst not supporting variation selectors in math, as was already mentioned in multiple instances.

@mkorje on Discord:

because its multiple characters and so ends up going through the normal text layout

@mkorje on Discord:

we need to then allow styling of a char in math to return possibly multiple characters. And also need to add the code to perform the glyph substitution somewhat manually (in line with everything else in math as it doesn't go through the shaper)

Some of the necessary changes are included in #20.

[Enivex]

Note that this is currently blocked by Typst not supporting variation selectors in math

Arguably that's only a blocker for support in math. It doesn't prevent them from being used in regular text

[EpicEricEE]

Maybe it's also worth mentioning that variation selectors currently don't seem to work at the end of a line (typst/typst#5319). While this isn't much of a blocker, I suppose that the end of a line is were emojis are commonly placed.

[Enivex]

There's a full (?) list of emojis that have text forms here https://www.unicode.org/Public/UCD/latest/ucd/emoji/emoji-variation-sequences.txt

We should make sure any symbol on the list has appropriate selectors in both sym.txt and emoji.txt, regardless of what the default is.