Docs: Synchronize documentation for `wp_get_attachment_image_attributes` filter callbacks in bundled themes:
* Twenty Sixteen: Correct the `$attachment` parameter type, use typed array notation.
* Twenty Seventeen: Correct the `$attachment` parameter type, use typed array notation.
* Twenty Nineteen: Correct the `@return` value type, use typed array notation.
* Twenty Twenty-One: Add missing `@return` value description, use typed array notation.
Follow-up to [29836], [47249], [49021], [49597].
Props ankitmaru, mukesh27, SergeyBiryukov.
Fixes #53878.
Built from https://develop.svn.wordpress.org/trunk@51607
git-svn-id: http://core.svn.wordpress.org/trunk@51218 1a063a9b-81f0-0310-95a4-ce76da25c4cd
a2a8b77806