Keywords and separators

[Felienne]

We have started to add separators in the keyword files directly, for example like this:

https://github.com/Felienne/hedy/blob/0999cf2146d228da384c69a08d2b017abac97821/grammars/keywords-nl.lark#L1

This is nice, because it keeps the grammar itself more readable but... if we want to generate the keyword files for new languages, we have to generate these separators as well. I was working on automating this (in #2615) but there are a lot of different cases and the generation has become too complex. What shall we do? I see a few paths forward:

1. Make the keyword grammars by hand, it is not a lot of work and it is not needed often, only when adding a new language
2. Make a template file and generate with that
3. Add a new file to the grammar that is only the keywords and rename the one we have to separators.lark and make that language agnostic.

I was leaning to 3, I almost started implementing it but maybe it is just a lot of work to only save 5 mins of manual work?

Tagging @jpelay who might have opinions here?