When `WP_Term` was introduced in [34997], the `$taxonomy` parameter for
`get_term()` was made optional. This meant that, when the optional param was
omitted, `get_term()` had no way of determining which term was intended when
the term_id was shared between multiple taxonomies. As a (somewhat sneaky) way
of fixing things, `get_term()` split any shared terms it found. But this could
cause problems with developer expectations: it's not clear why requesting a
term should result in a database update, much less a potential change in the
ID of a term.
In place of this technique, this changeset introduces a number of changes that
make the handling of shared terms a bit less insane:
* When a taxonomy is provided to `get_term()`, and a cached term is found matching the term_id, make sure the taxonomy also matches before returning it.
* When a taxonomy is not provided, ensure that the term is not shared before adding it to the cache.
* When a term is shared between taxonomies and no taxonomy is provided, return a `WP_Error` rather than splitting the term.
* When a term is shared between taxonomies, only one of which is valid, return the term from that taxonomy.
Props boonebgorges, dlh.
Fixes#34533.
git-svn-id: https://develop.svn.wordpress.org/trunk@35537 602fd350-edb4-49c9-b593-d223f7449a82
5043f0c795