Introduce register_post_status_for_object_type

[kovshenin]

Similar to what register_taxonomy_for_object_type does with taxonomies.

[sirzooro]

IMHO this should go to #12706.

[SergeyBiryukov]

Took a stab in 23169.patch​.

[kovshenin]

Replying to SergeyBiryukov: In 23169.patch​ you set the default post types to post and page, but there may be existing plugins that rely on their registered post status to apply to all post types, including custom post types. For backwards compatibility, I think that if the post_type/object_type argument is omitted in register_post_status, we should register for all post statuses, which can also be tricky, because at the time of calling, some post types might not be registered yet.