"being_used" predicate for items, to be used in resource packs

a "being_used" predicate for items would open a Lot of doors for what would be possible with resource packs, for example:

• making food look as though its being eaten when being eaten
• the spyglass using a separate model for when it's contracted/extended
• changing to an animated texture when an item is being used

there are already the "pulling" and "pull" values on bows and crossbows, but i think a general use "being_used" boolean would be just as useful considering the "consumable" item component.