clean_user_cache() doesn't clear the user_meta cache

[dd32]

Calling clean_user_cache() doesn't clear the user_meta cache, which can cause odd behaviours when the reason for calling it is that the user or usermeta DB tables have been altered.

Additionally, there is no API for clearing the metadata caches, other than performing a direct wp_cache_delete( $id, 'user_meta' );.

See attached PR.

Trac ticket: https://core.trac.wordpress.org/ticket/54316

This is intended as a simple version of #1776

Trac ticket: https://core.trac.wordpress.org/ticket/54316

I've refreshed this against trunk, but also opened #3447 which is a simpler straight to the point fix.

Closing in favour of #3447

Just noting that I've force-pushed this around a little to run a unit test that fails (for users, passes for posts) first, and then the original commit on top of that showing the unit test passing.

Posts passed originally as clean_post_cache() calls the same wp_cache_delete(), see ​https://github.com/WordPress/wordpress-develop/blob/trunk/src/wp-includes/post.php#L7373

[spacedmonkey]

This looks good to go to me. Adding commit keyword.

[spacedmonkey]

In 54940:

Users: Clear the user_meta cache when clean_user_cache function is called.

Unlike other clean cache functions like clean_post_cache, clean_user_cache did not also clear user meta caches. This is inconsistent and can result in some strange side effects. Update the clean_user_cache function to also clear user meta caches when called.

Props dd32, spacedmonkey, peterwilsoncc.
Fixes #54316.

Committed