Use 'theme_files' cache group for block pattern caches. Previously, block pattern cache data was not stored in a cache group and used the default group. This new cache group, is setup as a global cache group, meaning that sites using multisite, will have a single cache for block pattern data per theme. This change also no longer invalidate block pattern caches in multisite instances, meaning block pattern caches can be shared between sites on a network, meaning less repeated data in the object cache.
Props spacedmonkey, flixos90, joemcgill.
Fixes#60120.
git-svn-id: https://develop.svn.wordpress.org/trunk@57608 602fd350-edb4-49c9-b593-d223f7449a82
9a8d2c4dba