Item models held by foxes cannot be customized independently of dropped item models

Causes MC-276753.

The bug

Any rotation, translation and scale values provided to the "ground" display type of an item will also change how it is displayed when held by foxes. It is impossible to customize these independently of each other, and what looks acceptable for dropped items may end up looking strange for foxes (e.g. MC-276753).

How to reproduce

A resource pack that makes basalt huge and rotated when dropped on the ground is attached to this ticket.

1. Download and apply the attached resource pack

2. Drop basalt on the ground

3. Make a fox pick it up

Expected results

Basalt would look big as a dropped item but not when the fox picks it up.

Actual results

It still looks huge when the fox picks it up.

How to fix

Add a new display parameter to item models specifically for foxes. If left unspecified, it would default to whatever is specified for the ground display type, for backwards compatibility, but would be customizable independently of it if desired.