Added the `$post` parameter in attachment_submitbox_misc_actions and post_submitbox_start action

[sebastian.pisula]

Added the $post parameter in attachment_submitbox_misc_actions and post_submitbox_start action

[ericlewis]

$post is passed through post_submitbox_misc_actions action callbacks since r34895. Seems like these would be good for parity.

[SergeyBiryukov]

#40182 was marked as a duplicate.

[SergeyBiryukov]

36206.2.patch​ is a refresh that includes @tosho's patch from #40182 (with @since entry).

It also passes $post to media_submitbox_misc_sections and audio_submitbox_misc_sections actions for consistency.

Note that post_submitbox_start is also used in link_submit_meta_box(), which doesn't have a WP_Post object, but has a link object instead. Should we pass the link object in that case or just null? Current patch does the former.

[jbpaul17]

Punting to 4.8.1 per today's bug scrub.

[SergeyBiryukov]

Replying to SergeyBiryukov:

Note that post_submitbox_start is also used in link_submit_meta_box(), which doesn't have a WP_Post object, but has a link object instead. Should we pass the link object in that case or just null? Current patch does the former.

On second thought, the latter makes more sense.

[SergeyBiryukov]

In 41581:

Posts, Post Types: Pass $post parameter to post_submitbox_start, attachment_submitbox_misc_actions, media_submitbox_misc_sections, audio_submitbox_misc_sections filters.

Props sebastian.pisula, SergeyBiryukov.
Fixes #36206.