Includes:
* Documenting the returned array using hash notation.
* Adding a `@since` note for the `$filesize` value being included in the returned array.
This affects:
* `wp_generate_attachment_metadata()`
* `wp_get_attachment_metadata()`
* `WP_Image_Editor::save()`
* `WP_Image_Editor_GD::save()` and `::_save()`
* `WP_Image_Editor_Imagick::save()` and `::_save()`
Follow-up to [22094], [22619], [52837], [53546].
See #55646.
Built from https://develop.svn.wordpress.org/trunk@53547
git-svn-id: http://core.svn.wordpress.org/trunk@53136 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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