Add support for embedding PDFs

[westonruter]

Feature description

Gutenberg 10.5 adds support for embedding PDFs in the File block: WordPress/gutenberg#30857.

It does so by adding an object element to the page:

<object
	className="wp-block-file__embed"
	data={ href }
	type="application/pdf"
	style={ {
		width: '100%',
		height: `${ previewHeight }px`,
	} }
	aria-label={ pdfEmbedLabel }
/>

We need to add an AMP_Object_Sanitizer which automatically converts object[type=application/pdf] into amp-google-document-embed.

We also need to dequeue the new wp-block-library-file script which is getting enqueued in the render_callback, so dequeuing will need to be done at the wp_print_footer_scripts action. Or otherwise, we can just unset the render_callback entirely so that the $content is just passed through as-is.

---

Do not alter or remove anything below. The following sections will be managed by moderators only.

Acceptance criteria

Implementation brief

QA testing instructions

Demo

Changelog entry

[westonruter]

Another implementation option, aside from a new sanitizer, would be to extend AMP_Core_Block_Handler. It could add a new entry to \AMP_Core_Block_Handler::$block_ampify_methods to override the output, and then also to eliminate the render_callback on that block to prevent the script from being enqueued.

On the other hand, adding a sanitizer would allow for any object[type=application/pdf] to be made AMP-compatible, not just those appearing in a File block.

[pierlon]

I've ran into a small issue with this. The amp-google-document-embed component is using the Google Docs Viewer to display the PDF. The problem is that this won't work if the PDF URL is not publicly accessible.

[westonruter]

I think that is fine, if the problem is just that it's not working for you because the file is only on your local machine.