Deprecated get_all_category_ids() call can return incorrect results

[johnjamesjacoby]

In WordPress 4.0.0 and r28679, the get_all_category_ids() function was formally deprecated.

Internally, it continues to rely on a cache key (all_category_ids) that will never be repopulated.

This means anyone still using this deprecated function (yikes, I know...) on an installation with a persistent object cache is highly likely to be retrieving invalid/unexpected results.

[johnjamesjacoby]

Recommend to simply remove caching from this deprecated function completely.

At this point, anyone still using it is not likely doing so for the performance benefit, and get_terms combined with WP_Term_Query now provides caching by default.

[itowhid06]

remove caching from get_all_category_ids function

[SergeyBiryukov]

Some history on the 'all_category_ids' cache key:

• Added in [3011/trunk/wp-admin/admin-db.php].
• Replaced with clean_category_cache() in [4631].
• Removed in favor of clean_term_cache( $id, 'category' ) in [5555].

[SergeyBiryukov]

In 46810:

Taxonomy: Remove redundant caching from get_all_category_ids(), deprecated in favor of get_terms() in [28679].

The all_category_ids cache key it relied on was removed in [5555] and never repopulated, causing invalid or unexpected results when using a persistent object cache.

Props itowhid06, johnjamesjacoby.
Fixes #48176.