migrate EBNF codegen to DSL v2

[OmarTawfik]

leaving the older ebnf codegen in place until codegen_spec is migrated as well.

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Latest commit: c45b81e

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[Xanewok]

Looks good! I have some readability nitpicks in builder.rs that I'd like to see addressed, if you don't mind 🙏

[Xanewok]

I was confused by the SimpleEbnfWriter and didn't mean to block you on minor stuff. I'm approving not to induce churn - feel free to either re-add it to the queue or make the helper enums Copy to reduce some of the sigils in call-sites.