Document engine support

[Gerrit0]

Some discussion in PRs that I happened to notice seems to indicate that Shiki plans to require Node versions which are newer than the current maintenance LTS release (18, for the next few months)

It would be greatly appreciated if the supported Node versions were documented either on the website or via an engines field in the package.json file.

It would be even better if this behavior was validated by running CI on that version as well.

[slevithan]

I believe the context you're referring to was for the new JavaScript engine. However, @antfu and I made changes that avoided relying on Node 20 for the new engine. When it was actually released in Shiki 1.23.0, it required only Node.js 10 to run the generated regexes (since environment support for regex features is detected automatically by the default target: 'auto'). The only case when it requires Node.js 20+ is if you manually change the target option to ES2024 or later.