Redistribute Built-in components and remove page

[sarah11918]

Description (required)

This PR removes the Built-in Components reference page entirely in favour of redistributing the components to appropriate pages in docs.

(These components were not very similar to each other, did not all require imports, and in some cases were duplicate content existing in guides already.)

In the process:

• Creates a new Syntax Highlighting guide for both Markdown code block advice with the Code and Prism components which otherwise didn't have a super obvious place to go. This alleviates some of the content in the Markdown guide and describes all code syntax highlighting options together
• Moves markdown.shikiConfig content to configuration reference rather than having that entry link to the Markdown guide (in-branch overwrite right now, until we know what we want at the source)
• Makes the syntax highlighting content more "guide" like
• removes some "asides" in favour of proper documentation of "how things work"

Note: If we don't like the experiment of syntax highlighting as its own guide, this content can go back to the Markdown guide page. However, we would need to decide on a better place for the two Code and Prism components

UPDATE: The experimental changes above were well received on Talking and Doc'ing, so going with this overall structure for now!

• Structure for new syntax higlighting page
• file name and page title for new syntax highlighting page
• deal with link fall out
• remove component reference page from all i18n/nav pages that had it
• LUNARIA TRACKING STATEMENT

Follow up:

• Make a PR for configuration reference (astro main branch) with the new Shiki config reference (PR here)
• If someone wants to make it actually reference-y at some point/in the process, that's fine too!