Patch for CM5 native CSS nesting highlighting

[Gazook89]

Description

As described in issue #4655 CM5 doesn't highlight nested selectors.

The CSS mode included with CM5 has two sub-modes, x-LESS and x-SCSS, and they have a allowNested property set to true. So I took that and popped it into the base CSS mode as well, and it worked.

This adds patch-package to the dev dependencies, and after any npm install it patches node_modules/codemirror/mode/css to modify the CSS mode to include allowNested option, set to true.

Could this be done in a cleaner way, perhaps by modifying the language mode within our editor instance? Maybe. I tried. I couldn't find where I could access or add a allowNested option.

There are a few other things we could modify in the css mode in the same way like newer css properties, selectors, etc. This is just a trail balloon, though.

[calculuschild]

Patching the npm package feels a bit sketchy. I can see the CSS mode doesn't expose the allowNested option, but can we do something like this in our codeMirror setup to kind of wrap the old CSS mode in a custom mode and change it there?

// Get original mode
const origCssMode = CodeMirror.modes.css;

// Override it with a version that exposes the allowNested mode
CodeMirror.defineMode("css", function(config, parserConfig) {
  const mode = origCssMode(config, parserConfig);
  mode.allowNested = true;        // <- see if something like this works?
  return mode;
});

[Gazook89]

Yes that seems to work just fine. I tried to figure something out like that, but couldn't get it work, so thanks. Feel like a dummy.

[calculuschild]

Yes that seems to work just fine. I tried to figure something out like that, but couldn't get it work, so thanks. Feel like a dummy.

Ok, in that case could you remove the patch-package dependency and then we can merge this?