Replace `mdx-bundler` with `@mdx-js/esbuild`

Seems like MDX v2 is just around the corner so we should investigate upgrading to it soon.

We should also verify whether mdx-bundler is still needed with MDX v2.

[marcofranssen]

Note: Practically speaking Contentlayer users should already be using MDX v2 today.

What do you mean by this Note? How can/should we practically use MDX v2?

[schickling]

Update: I’ve started investigating replacing mdx-bundler with @mdx-js/esbuild however this doesn’t seem to be entirely trivial given esbuild.build() expects a “physical” file path instead of an input string (which is what the current Contentlayer implementation is structured around). This is something mdx-bundler is providing out of the box which is why I’ll stick to mdx-bundler for the time being (until this becomes easier to do - or there’s another reason to do so).

Once https://github.com/kentcdodds/mdx-bundler/pull/152 I’ll update the mdx-bundler dependency.

Note: Practically speaking Contentlayer users should already be using MDX v2 today.