Back compat $_REQUEST['post_id'] for media XHR requests

[nacin]

query-attachments, save-attachments, and save-attachments-compat should all pass back 'post_id', for consistency with the old media-upload.php dialog, as plugins may be doing $_REQUEST['post_id'] checks in conjunction with parse_query, save_post, attachment_fields_to_save, or other filters.

We should consider also calling set_current_screen( 'media-upload' ) for these three requests, or for at least query-attachments, to allow the current screen object to be accurate. It's kind of hacky, and doesn't handle $pagenow, but it is something to consider.

[koopersmith]

Patch adds support for $_REQUEST['post_id'] in all media ajax requests.

[koopersmith]

Ignore that. Parts of the patch confuse the post ID we're acting on with the post ID context (the post we're editing while we perform the action).

[koopersmith]

Let's try this again.

[nacin]

Untested, but that looks lovely.

[nacin]

#22582 was marked as a duplicate.

[nacin]

Refreshed to add post_id to send-link-to-editor too.

[nacin]

Tested before and after, logging the ajax requests. Looks good.

[ryan]

In 22865:

Back compat $_REQUESTpost_id? for media XHR requests.

Props koopersmith, nacin.
fixes #22588