Modify the_editor to Properly Allow Multiple Instances on a Page

[xazure]

Currently, the_editor() is essentially hard-wired to only allow one instance per page (because of it's use of id's and such).

It would be nice if the_editor was modified to properly allow for multiple instances.

The change would essentially involve changing all of the IDs to use classes instead (which can allow multiple instances on one page), and adjusting any Javascript appropriately.

Most (if not all) of these changes would take place in the_editor() function, found in /wp-includes/general-template.php starting at line 1789.

See #17144.