Adds data-lang attribute for CommonMark code block renderer

[alexgarrettsmith]

This PR adds a data-lang attribute to CommonMark code blocks, allowing an unobtrusive method of accessing the currently highlighted language for display purposes.

For example (in this case with Tailwind typography), the prose-pre:after:content-[attr(data-lang)] class could be used to style a pseudo element with the following result (top right):

I've avoided adding this to pre output and InlineTheme output for simplicity, but happy to add this in if needed.

[coveralls]

Pull Request Test Coverage Report for Build 8525924001

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.608%

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Totals
Change from base Build 8522176271:	0.0%
Covered Lines:	1316
Relevant Lines:	1391

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💛 - Coveralls

[aidan-casey]

Thanks for the PR, @alexgarrettsmith!

@brendt, we should keep #81 in mind for this. If the alias is used, would the expected behavior be that the alias is set or the primary language key?

[brendt]

If the alias is used, would the expected behavior be that the alias is set or the primary language key?

@aidan-casey for now I think this is fine. Languages currently don't define their own code(s), and we cannot change that without a breaking change. So using the language code directly is ok. I plan on changing this in the future.

I've avoided adding this to pre output and InlineTheme output for simplicity, but happy to add this in if needed.

@alexgarrettsmith This is actually a pretty big oversight on my part, because the theme itself has no idea about the current language. I can add an ugly string replace as a temporary fix within the common mark renderer, but I think I have a better idea (described in #91) This would require a breaking change though.

What I think I'll do is merge this in, and only have support for it on themes without WithPre. I don't scare away from tagging a new major quickly, so I'll probably have this fixed in v2 somewhere this week of next.

[brendt]

Tagged: https://github.com/tempestphp/highlight/releases/tag/1.3.0

[alexgarrettsmith]

No worries @brendt, I noticed that the language wasn't available there which is why I didn't touch it — appreciate that you're heavily developing right now and didn't want to get in the way.

Appreciate the merge!