Drop support for ESLint < v8.44

[ota-meshi]

I noticed that ESLint's standard parser can't parse the v flag until ESLint is updated to v8.44.
This PR drops support for ESLint < v8.44.

https://eslint.org/blog/2023/06/eslint-v8.44.0-released/

We could leave the old ESLint support and check the ESLint version, and branch whether or not to test for the v flag, but I think it would be expensive to do that. So I think it makes more sense to drop the old ESLint support.

[changeset-bot]

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eslint-plugin-regexp	Major

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[RunDevelopment]

Why exactly would we need to check the ESLint version and branch?

The ESLint parser AST represents regexes as { pattern: string; flags: string }, so why does it matter to us whether the parser supports the v flag? The only issue I see is that rules that add the v flag to regexes (probably a use-v-flag rule) will create code that ESLint can't parse. But that's not our problem. We produce valid JS/TS, and users can turn off the rule if it causes issues.

[ota-meshi]

The old parser will throw a parsing error with the v flag as an unknown flag. Parsing the v flag requires espree v9.6.0 and is definitely included in eslint v8.44.0 and later.

https://github.com/eslint/espree/releases/tag/v9.6.0

That said, we can certainly use new RegExp('pattern', 'v') if we just want to test our rule.

[RunDevelopment]

That said, we can certainly use new RegExp('pattern', 'v') if we just want to test our rule.

Oh, so we can't even properly test our v-flag rules right now? That certainly is an issue, and I don't like the idea of having to use RegExp('pattern', 'v') everywhere. We still won't be able to use regex literals in test, because NodeJS 18 doesn't support the v flag, but String.raw`/pattern/v` is better than String.raw`new RegExp('pattern', 'v')`.