spectacle-mdx-loader: MDX component map lacks a lot of things that Markdown supports

We have a discrepancy in code blocks in MD vs. MDX and likely other Spectacle core component support.

## Example

For our MD example with `pnpm start:md` for the code page we have:


For our MDX example with `pnpm start:mdx` for the code page with exact same sample we have:


## Cause

Our `Markdown` component and related components do a **lot** more things than our `mdxComponentMap` does that we pass into MDX.

## Work

See if we can expand `mdxComponentMap` to something more general that ideally doesn't rejigger core Spectacle too much.