feat: monaco editor folding range provider

[adamdehaven]

Summary

Add a monaco-editor folding range provider to support folding mdc block components. Usage example has been added to the Editor.vue and README.

Originally, I was going to implement via the languages.LanguageConfiguration property as shown here:

folding: {
  markers: {
    start: /^\s*:{2,}([\w-]+)/, // Matches opening tags like "::component"
    end: /^\s*:{2,}$/, // Matches closing tags like "::"
  },
},

However, the implementation requires a custom folding range provider since we want to match the number of colon : characters for opening and ending tags.

This PR also updates the formatter to support ``` and ~~~ for code block fences.

Examples

MDC content:

# Code Folding

::container
  :::child-component
  Child component text
  :::
::

Hover state

Collapsed child block component

Collapsed parent block component

[farnabaz]

Looks perfect 🔥