Add new filter post_gallery_results to replace the core gallery template after the attachment query

[jeremyfelt]

The post_gallery filter in gallery_shortcode() already allows complete replacement of the gallery template provided by core. However, any function attached to this filter must also handle the query logic for attachment data.

The proposed filter post_gallery_results is placed immediately after all query logic is complete. The gallery template output can still be replaced, but with the help of the $attachments data provided by core queries.

[jeremyfelt]

Additional filter for post_gallery_results in media.php

[TomAuger]

Looks like an exact duplicate of #14130, except that he's putting the filter after the feed() check, instead of before.

However, I prefer #14130 because it also includes the $attr parameter, which is pretty critical if you're going to be rolling your own HTML output.