The data stored in the cache should be raw database query results, not
`WP_Term` objects (which may be modified by plugins, and may contain additional
properties that shouldn't be cached).
If term relationships caches were handled in `wp_get_object_terms()` - where
a database query takes place - it would be straightforward to cache raw data.
See #34239. Since, in fact, `get_the_terms()` caches the value it gets from
`wp_get_object_terms()`, we need a technique that allows us to get raw data
from a `WP_Term` object. Mirroring `WP_User`, we introduce a `data` property
on term objects, which `get_the_terms()` uses to fetch cacheable term info.
Fixes#34262.
git-svn-id: https://develop.svn.wordpress.org/trunk@35032 602fd350-edb4-49c9-b593-d223f7449a82
ed4eee668e