feat(math): Support the MathML operator dictionary and many TeX-like aliases

[Omikhleia]

WIP for now, still things to check and fix, but most of the stuff is starting to work well... So it's good "saving checkpoint" to share.

Good to go, IMHO 🚀

First commit

• Lots of refactoring in the atom / types logic... and some code clean-up.
• The operator dictionary table (for MathML), and most of the TeX-like commands (for that syntax), are now based on the W3C xml-entities unicode.xml with the diff patch from this issue applied.¹
  • It ticks yet another checkbox in Math operators: stretchy or not stretchy #2148 🐱
  • Lots of "big"-operators and extra integrals are now supported
    Eg. \coprod, \bigcupdot, \intclockwise and all their friends do the expect magic.
  • Lots of additional TeX-like commands (\circ, \pod, etc. to just mention a few) are supported.
  • More "stretchy" operators work (... but not all yet, and proper support for accents will come later....)
  • "form" attribute on MathML mo and a first take at "embellished" operators (paving the way for another checkbox in Epic: Unsupported MathML elements and attributes #2138 eventually, though we are not there yet...)

Subsequent commits

Ah, the operator table makes many things better, but others are worse...

• fix(math): Spacing rules must distinguish binary and unary operators --> Needed consequence of making the minus-hyphen (U+002D) equivalent to the minus sign (U+2212) for math purposes. An occasion to also kill an old issue...
• fix(math): The (escaped) percent is an ordinary atom in TeX-like syntax --> The former behavior had it encoded as a binary operator, it's now aligned with what (La)TeX would produce.
• fix(math): A period must be allowed in TeX-like math syntax for numbers --> Decimals 0.123 later seen as <mn>0.123</mn> instead of <mn>0</mn><mo>.</mo><mn>123</mn> (with period as punctuation in MathML, possibly affecting spacing)
• Some tests have been re-aligned / cleaned after analysis = all math tests are passing again.

Then..

• fix(math): Improve spacing rules on limit-like operators --> Includes a refactor...
• ... and more refactoring follows on those atom types with too many names ^^ = KISS 😽 a thing shall have one name only.
• feat(math): Add pre-defined TeX-like operator functions (cos, sin, etc.) --> Bonus cake 🍰
• docs(math): Update description of atoms and TeX-like pre-defined constructs

Issues addressed

Closes #1642

Closes #2169

Parts of some other issues are mentioned above. We're getting closer.

Footnotes

1. The converter/extractor (in XSLT 1.0 i.e. xsltproc-compatible) from unicode.xml to our Lua structures is included too in the PR. ↩

[Omikhleia]

@alerque Good for review, in my opinion.
I have a few other commits that build upon this nice baby, but they are more controversial and I'll likely open dedicated issues before pushing a proposal.

[Omikhleia]

@alerque Good for review, in my opinion. I have a few other commits that build upon this nice baby, but they are more controversial and I'll likely open dedicated issues before pushing a proposal.

Oh wait, on a second thought (when I annotated the "unused" atom types above...) I just realized we can clear it up a bit here, with a good gain: bigOperator is ill-named from the start, it's corresponding to TeX mathop (with respect to spacing rules) and all of a sudden something becomes much clearer.

[Omikhleia]

Now this is much better, with bonus cakes 🍰 and tests 🧪

[alerque]

Force push so far just to fix Lua style (BTW stylua 2.0.0 has been released that works with this project's style options). No chance for deeper review yet.