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.

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

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).

Let's try this again.

Untested, but that looks lovely.

#22582 was marked as a duplicate.

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

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

In 22865:

Back compat $_REQUESTpost_id? for media XHR requests.

Props koopersmith, nacin.
fixes #22588