CommonMark code block class names

[remyrylan]

This is a very simple fix that changes TypeDoc to follow the CommonMark spec for code blocks:
https://spec.commonmark.org/0.27/ Example: https://spec.commonmark.org/0.27/#example-109

Right now TypeDoc prints out code block prefixes with lang- as the prefix, which is far I understand it, is legacy from Highlight.js. Since TypeDoc uses Highlight.js, lang-, language- and even un-prefixed values are supported... But by enforcing the CommonMark standard developers will be able to leverage other CommonMark tools with TypeDoc.

[remyrylan]

Looking at the tests and there are a ton of failings in there that are unrelated, looks like the CI environment needs some attention.

Edit: Just checked and everything passes for me locally. I did notice that running npm run test does automatically update the test files, so both src/test/renderer/specs/classes/_default_export_.notexportedclassname.html and src/test/renderer/specs/index.html are automatically updated to use language-* instead of lang-*

Let me know if need me to update those tests by hand or I should let it be and some automated process handles it?

[aciccarello]

The changes you've included so far sound good. Yeah, I'm aware of the test issues. #762 includes some fixes to how the tests are run so they aren't overwritten. I'll need to review why the models changed in the snapshot tests and correct things in a separate PR so leave things as they are until those are fixed.

[aciccarello]

Sweet. Looks like your markedjs/marked#1265 PR ended the need for this. Thanks for your contributions! The updated specs now use the updated prefix

typedoc/src/test/renderer/specs/index.html

Lines 78 to 81 in eace04a

	<pre><code class="language-bash">$ npm install typedoc --save-dev</code></pre>
	<p>Like the TypeScript compiler, TypeDoc comes with a binary that can be called from anywhere
	if you install TypeDoc as a global module. The name of the executable is <code>typedoc</code>.</p>
	<pre><code class="language-bash">$ npm install typedoc --global