Add lazys symbol and variants

[MDLC01]

This adds new lazy S symbols from Unicode 18.0.

Relevant links:

• Unicode 18.0 Mathematical Operators delta chart
• Unicode 18.0 Supplemental Mathematical Operators delta chart
• The Symbol list for sym document, which contains a Lazy S section as of writing this.

This PR is related to, but independent from, #181.

[Enivex]

Could we use just lazy instead of lazys? It looks less awkward, and as far as I'm aware doesn't conflict with anything.

[sijow]

I think just "lazy" would be too generic and cryptic for this. As I understand the name "lazy S" describes an S that's "lazy" because it lies down. "Lazy" alone doesn't make sense.

I agree though that lazys is weird. I also don't like that eq.rev would give a glyph with nothing obviously reversed.

[Enivex]

I was thinking more as a modifier to tilde, which is essentially how it is encoded.

As in

eq.tilde.lazy

[T0mstone]

In principle I like eq.tilde.lazy, but that would make lazy a modifier on eq. This is kind of like the situation of lt.eq.slant and I'm not sure I want to add more modifiers like that.

Also if we do have it as such a modifier, what about .s instead of .lazy?

[MDLC01]

The lazy S is not a lazy tilde, it's a lazy S. I do agree that the name "lazys" is a bit awkward because it is hard to interpret what it means if you don't already know what a lazy S is, but it is still the best name imo. In particular, I don't really see a point in making it a variant of tilde instead of its own symbol.

Also, note that a regular lazy S corresponds to a reversed tilde, so tilde.lazy would be a reversed lazy S, and tilde.rev.lazy a regular lazy S.