Make sure `$post` is properly documented as optional where applicable.

See #28388.

Built from https://develop.svn.wordpress.org/trunk@28653


git-svn-id: http://core.svn.wordpress.org/trunk@28471 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Ensure `$post_id` is documented as optional where applicable.

See #28388.

Built from https://develop.svn.wordpress.org/trunk@28654


git-svn-id: http://core.svn.wordpress.org/trunk@28472 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Be more specific that `$post_id` does not default to the ID of the global `$post` in some cases.

See [28654]. See #28388.

Built from https://develop.svn.wordpress.org/trunk@28655


git-svn-id: http://core.svn.wordpress.org/trunk@28473 1a063a9b-81f0-0310-95a4-ce76da25c4cd