Fixes for #3018, [each] tag traversal does not work with taxonomy (2.x)

[pglewis]

2.x branch patch for #3018

Needs review.

[scrutinizer-notifier]

A new inspection was created.

[sc0ttkclark]

Sorry, merged before I saw that you should be looking at $pod->object_fields and not $pod->fields for taxonomy fields. Can you update the branch and submit a new PR? I'll leave the 3.0 one unmerged for the same reason too.

[sc0ttkclark]

Let's add a code comment above the field() call that calling field() for a taxonomy object field will populate $pod->fields[ $field_name ] for the object field's data, in this case a taxonomy object field. Without calling $pod->field( $field_name ), it would not normally be available in the $pod->fields array and is something to not expect to be there in 3.0 as this was unintentional.