Improve cleanup of cached term_ids after shared terms are split.

* If the split term ID is stored as 'default_category', 'default_link_category', or 'default_email_category', update it to the new ID.
* If the split term ID is associated with a nav menu item, update that piece of postmeta to the new ID.

Props mboynes.
See #30335.

git-svn-id: https://develop.svn.wordpress.org/trunk@30494 602fd350-edb4-49c9-b593-d223f7449a82