Allow AlpineJS syntax extensions in Markdown

[hippotastic]

Changes

• Fixes 🐛 BUG: Alpinejs bind shorthands (ex. :width="<expression>") in markdown error dev and build #3517.
• Uses our new scoped package @astrojs/micromark-extension-mdx-jsx as a replacement for micromark-extension-mdx-jsx. This package contains modifications to the Markdown MDX/JSX tokenizer that allow the AlpineJS syntax to work again.
• Adds tests for the new syntax.

Testing

• Added new test cases to cover all relevant cases of the AlpineJS syntax based on their docs.
• Successfully ran all tests locally.
• Built Astro Docs with the new packages.
• Built a sample Astro project that contains the AlpineJS example code from their homepage in a Markdown file, and the resulting page worked.

Docs

• Not a visible change.

[changeset-bot]

🦋 Changeset detected

Latest commit: 85b059d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@astrojs/markdown-remark	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[hippotastic]

@natemoo-re PTAL :)

[natemoo-re]

Looks great! Just had a few questions.

[natemoo-re]

LGTM!