feat: improved syntax highlighting for the solidity language

[erunion]

🚥 Fixes RM-7006

🧰 Changes

When I added support for the Solidity language¹ in #219 I pretty half-assed it by treating all code in that language as C-like, which is sort of true as it does has elements of C. In reality, this ends up treating most every keyword and aspect of the language as a C language comment or a variable, resulting in everything being highlighted as green:

There's a codemirror-solidity library that handles this as it should² but unfortunately it can't be imported in here because of the way that it defines its Codemirror mode³. Because of this, I've pulled that source over into this library, added attribution where necessary, and updated our Solidity example to better reflect real-world usage of the language⁴.

tl;dr: Our Solidity highlighting sucks, is better now.

Footnotes

1. Solidity is for blockchain programming. ↩

2. https://alincode.github.io/codemirror-solidity/ ↩

3. https://github.com/alincode/codemirror-solidity/blob/master/index.js ↩

4. https://docs.soliditylang.org/en/latest/solidity-by-example.html ↩