Allow pasting a bare PDF URL to enable an inline, visual PDF file embed directly in post/page content.

Currently with WordPress sites you can add a PDF file via the Media Library, and you get a linked file reference.

Or, you can make a full URL link to show it's a PDF.

Both cases don't embed the actual PDF file for easy viewing right in the post.

This new feature would add an embed handler for PDF files. Pull request to come.

Context: we've had this as a hidden feature on WordPress.com for a few years, but only for Automatticians. Releasing this on WordPress.com soon, and want to match the behavior in Jetpack for Atomic sites, too.