Fix MDX + Tailwind, add support for injected page-ssr scripts to MDX extension

[FredKSchott]

Changes

• This is a short-term fix to add basic script injection handling to the MDX integration, to unblock MDX + Tailwind.
• I call it short term because this is code that we've identified as a copy-paste risk that I've now pasted into a third place. On top of that, it is missing some logic to only inject the page script on MDX pages, and not non-page MDX files. That is considered a larger regression that will probably need a larger refactoring to solve for. In the meantime, this unblocks a v1.0 RC release.
• With this I now see tailwind working with .mdx, .md (legacy), and .md (current)

Testing

• Added a test.

Docs

• N/A

[changeset-bot]

🦋 Changeset detected

Latest commit: a3e2cae

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

This PR includes changesets to release 5 packages

Name	Type
@astrojs/mdx	Patch
@e2e/preact-component	Patch
@e2e/react-component	Patch
@e2e/solid-component	Patch
@e2e/svelte-component	Patch

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[FredKSchott]

Got @natemoo-re's +1 on Discord