Add support for styling U+2126 OHM SIGN

[MDLC01]

U+2126 OHM SIGN canonically decomposes to the regular capital Omega Greek letter. For this reason, I believe it should behave just like the regular capital Omega with regard to styling.

[mkorje]

IMO it'd be cleaner to add a new function like conversions::normalize, which converts the ohm sign to captial omega, and then call that at the top of MathStyle:select and to_style.

[MDLC01]

I did that. Also, I was not able to find any other character that we might want to normalize (i.e., a character that canonically decomposes to a character that we can style), but I did not do any form of exhaustive check.

[Enivex]

U+212A maps to a regular K

https://www.compart.com/en/unicode/U+212A

There's also all the precomposed letters. For instance, bold() does not work on Å (precomposed), but it does work* on Å (using combining character).

*bold is currently broken when applied to combining accents, which I will report if it hasn't been already

[Enivex]

Another one: U+1FBE (Greek Prosgegrammeni) decomposes to a regular iota.

(Though I question if anyone would actually use that...)

If Google's AI result isn't lying to me, that should be everything stylable that's not CJK or contains accents.

[MDLC01]

I added support for U+212A and U+1FBE.