Feature Request: Giphy Unfurling

Unlike #138 which would be to support selecting a Gif with Giphy, this is to simply expand a shared Giphy link to show the animated Gif with the post. The URL appears to be consistent so it might be possible to quickly identify compatible Giphy links.

This shared link below will go to a page and within the page there are meta properties for Open Graph which could be used. Either og:url or og:image seems to work. There is also a video option which may have better performance when the Gif file is bigger. Determining which once to use could be handled with an HTTP HEAD request to get the size. The og:title could be used for Alt text for anyone who is visually impaired. This same behavior may work with any linked page which offers Open Graph properties.

https://media.giphy.com/media/kPy9ghQeyBXWsBJ6DI/giphy.gif

<meta property="og:site_name" content="GIPHY">
<meta property="og:url" content="https://i.giphy.com/media/kPy9ghQeyBXWsBJ6DI/giphy.gif">
<meta property="og:title" content="Community Freedom GIF - Find &amp; Share on GIPHY">
<meta property="og:description" content="Discover &amp; share this Yin Woods GIF with everyone you know. GIPHY is how you search, share, discover, and create GIFs.">
<meta property="og:type" content="video.other">
<meta property="og:image" content="https://i.giphy.com/media/kPy9ghQeyBXWsBJ6DI/giphy.gif">
<meta property="og:image:type" content="image/gif">
<meta property="og:image:width" content="480">
<meta property="og:image:height" content="480">
<meta property="og:video" content="https://i.giphy.com/media/kPy9ghQeyBXWsBJ6DI/giphy.mp4">
<meta property="og:video:url" content="https://i.giphy.com/media/kPy9ghQeyBXWsBJ6DI/giphy.mp4">
<meta property="og:video:secure_url" content="https://i.giphy.com/media/kPy9ghQeyBXWsBJ6DI/giphy.mp4">
<meta property="og:video:type" content="video/mp4">
<meta property="og:video:width" content="480">
<meta property="og:video:height" content="480">

The issue names no files, tests, or entry points. Start by locating the existing shared-link or media-unfurling path and inspect how the supplied Giphy URL and its Open Graph metadata could fit there. Done should be demonstrated by the linked Giphy content appearing with suitable animated media and accessible text, with the chosen media behavior covered by tests.