[MDX] Support img component prop for optimized images

[bholmesdev]

Changes

Respect the img component prop / export for images optimized via astro:assets. This will pass an ImageMetadata object as the src property to any img component when an optimized image is used.

• Resolves img MDX component override is not used in Astro collections #7223
• Introduce an 'astro-image' custom element to map via the components prop
• Check for user components passed as props or via an export before applying the Astro image optimizer

Testing

• test components property as export, esm import, and content collection entry

Docs

• docs draft in CHANGELOG
• official docs still TODO until we decide we like this!

[changeset-bot]

🦋 Changeset detected

Latest commit: 783e31f

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

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[bholmesdev]

I'm debating if this is a major, since it will now pass ImageMetadata for optimized images (see changeset). Could be breaking, or just a "new feature" since we didn't respect the img export at all before this change 🤔

[natemoo-re]

major is probably safer given that users may need to update their existing code, but if users couldn't actually use img previously, I think minor makes sense.

Code LGTM.

[Princesseuh]

You went much further than I would've had I implemented this myself, awesome work!