Implement `wp_cache_*_multiple` functions

[spacedmonkey]

Implement new functions, wp_cache_add_multiple, wp_cache_set_multiple and wp_cache_delete_multiple functions.

https://core.trac.wordpress.org/changeset/52700

Not to mention https://make.wordpress.org/core/2020/08/11/introduce-wp_cache_get_multiple/

[spacedmonkey]

https://make.wordpress.org/core/2022/04/29/caching-improvements-in-wordpress-6-0/

[spacedmonkey]

@tlovett1 Any update on this?