Adds a new REST API endpoint (`/wp-block-editor/v1/url-details`) for retrieving information from an external URL.
Information retrieved:
* Title: content of the `<title>` element
* Icon: favicon image link
* Description: content of the `description` or `og:description` meta element
* Image: OG image link
This endpoint is used by the block editor for link previews.
Props get_dave, aduth, andraganescu, beaulebens, hellofromTonya, kevin940726, mamaduka, marekhrabe, mnelson4, noisysocks, obenland, ocean90, retrofox, shaunandrews, spacedmonkey, swissspidy, timothyblynjacobs, xknown, youknowriad.
Fixes#54358.
Built from https://develop.svn.wordpress.org/trunk@51973
git-svn-id: http://core.svn.wordpress.org/trunk@51562 1a063a9b-81f0-0310-95a4-ce76da25c4cd
