REF: avoid _internal_get_values in json get_values
cc @WillAyd 

As mentioned in #32731, this changes the behavior for CategoricalIndex[dt64tz] and Series with that for its index.  Suggestions for where tests for that should go?

Note: the Categorical[dt64tz] cases still do a trip through object-dtype; I don't want to futz with that in C-space.
> Suggestions for where tests for that should go?

Pretty much everything right now goes into `test_pandas`; there's a PR to start fixturing / splitting things that I promise I'll get back to...but for now just place there lgtm. happy if you guys are. Thanks @jbrockmendel