Deleting a term does not invalidate cache for child terms

[boonebgorges]

See #29614.

Steps to reproduce:

1. Create a $term in a hierarchical taxonomy
2. Create a $child_term with parent=$term
3. wp_delete_term( $term )
4. Fetch cached version of $child_term with get_term(). 'parent' is still $term.

Unit test attached.

Two options to fix:

1. During deletion, run a query to get term_ids of all child terms, then run each through clean_term_cache().
2. During deletion, instead of doing a direct DB query to change the parent, run each item through wp_update_term().

Option 2 is much more aesthetically pleasing, but in cases where a parent has hundreds of children, there could be scaling issues, as separate DB queries would be run for each. Could use some testing, and a patch.

[nacin]

Option 1 is what we do for posts. See wp_delete_post(). Very simple and straightforward.

[socki03]

Added clean term cache for the term's children.

[socki03]

I was able to replicate the issue, and my initial tests resolved it with this patch resolved it.

I noticed from the documentation, that clean_term_cache can accept an array of IDs, so I ran it once using the $edit_tt_ids variable instead of a foreach loop, as is done on the clean_post_cache.

[boonebgorges]

Thanks for the patch. You're right about clean_term_cache(). However, the ids passed to that function are expected to be term_id, not term_taxonomy_id.

[boonebgorges]

In 29945:

Invalidate cache for child terms when parent term is deleted.

Props socki03.
Fixes #29911.