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.