Move dots.h to .h.b to give precedence to .h.c

[knuesel]

It seems that having dots default to the centered version was meant to be implemented already in typst/typst#747 but that implementation was wrong (just changing the order of .h and .h.c without considering the number of modifiers).

Closes #147

[MDLC01]

Since I expect dots to be commonly used in math, I would suggest the following path that ensures a smooth transition:

• In the next version (i.e., this PR), introduce dots.h.b and deprecate dots.h, suggesting to use dots.h.b instead.
• In a future version, change dots.h to be the centered version and deprecate dots.h.c, suggesting to use dots.h instead.
• In a later version, completely remove dots.h.c.

That way, we ultimately end up with dots.h and dots.h.b and no dots.h.c.

Unrelatedly, I don't love the .b modifier here, but I don't have a better solution so it's probably fine. An alternative is to rename the current dots.h to ellipsis, but I think this is just confusing.

[knuesel]

Good idea. It wasn't clear to me this deprecation was possible but l guess there's no problem if we have two different lines for the same symbol.

I have the same feeling for .b. Another option would be to use dots.op for dots.h.c and dots.basic for dots.h.b. This would mirror the relationship between dot.op and dot.basic.

[dccsillag]

I think the deprecation plan is good.

Re. names, I also share the slight discomfort with .b, but I think it is better than ellipsis (because then it's less discoverable) as well as dots.op/dots.basic (dots.basic is a bit weird but not too bad, but dots.op is not an operator like dot.op is). Overall, I don't think it's that bad of a choice, especially considering it's just a "transition name".

[knuesel]

dots.op is not an operator like dot.op is

dots.op (U+22EF) has the "relation" class, so it's arguably considered an operator in Unicode in the same sense as > (unlike dots.b which has normal class) though it's indeed different from a binary operator like dot.op...

[MDLC01]

Overall, I don't think it's that bad of a choice, especially considering it's just a "transition name".

dots.h.b would not be a transition name though.

[T0mstone]

How about dots.h.low? We already have precedent for .low with ast.low (⁎) and quote.low.