Videos in plugin description get cut off

[philipjohn]

In the new plugin directory, if a plugin uses a video at the start of the plugin directory it gets cut off by the "Read More" feature.

This looks broken at first, until you realise it's just hidden. Not a bug in itself, but a UI weirdness. We perhaps need to be able to have an "excerpt" for that first snippet, but that's probably not an easy solution.

See ​https://wordpress.org/plugins-wp/liveblog/ for an example, and the attached screenshot.

[philipjohn]

Video is cut off

[samuelsidler]

So we probably need to autodetect if a video is starting off the Details section and resize the area to fit. We'll have to know the default sizes of the various video platforms we support.

[dd32]

In 4385:

Plugin Directory: Expand the initial description to show the full contents of any embed/videos present in the first paragraph/div.
This fixes cases where descriptions start with a video, and caused the controls to be hidden below the fold.

Fixes #1789.