Add code block inline marking, including ins & del marker types

[hippotastic]

What kind of changes does this PR include?

• Changes to the docs site code

Description

• Adds support for line marking definitions with an optional marker type prefix. Examples:
  • {4-5,10} (if no marker type prefix is given, it defaults to mark)
  • mark={4-5,10}
  • del={4-5,10} (new, marks a deleted line, alias name: rem)
  • ins={4-5,10} (new, marks an added line, alias name: add)
• Adds support for inline marking definitions inside forward slashes, with an optional marker type prefix. Examples:
  • /sidebar/ (if no marker type prefix is given, it defaults to mark)
  • mark=/sidebar/ (all common regular expression features are supported)
  • mark=/slot="(.*?)"/ (if capture groups are contained, these will be marked)
  • del=/src\/pages\/.*\.astro/ (escaping special chars with a backslash works, too)
  • ins=/this|that/
• Fixes various escaping issues by replacing our faulty escapeHtml/unescapeHtml functions with the battle-tested html-escaper package.
• Adds marker examples to framework-components.md:
  • Line & inline markers of add/ins type:
    
  • Marking regular expression capture groups:
    

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[hippotastic]

Looks like Netlify's Node.js version doesn't support the RegExp flag d which I'm using to get the indices of capture groups. Will need to find an alternative for that. :)

[hippotastic]

I added a fallback that seems to work well. https://deploy-preview-1160--astro-docs-2.netlify.app/en/core-concepts/framework-components/ :)

[delucis]

LGTM! This totally looks like another instance of “Hippo builds an entire useful ecosystem package inside docs” so like for the link checker, I’d encourage you to consider looking at wrapping this up as a “Rocket-fueled Syntax Highlighter” npm package so we can share the brilliance and make it easier to add tests etc.