Rename PickingBehavior to Pickable

[chompaa]

Objective

PR #17225 allowed for sprite picking to be opt-in. After some discussion, it was agreed that PickingBehavior should be used to opt-in to sprite picking behavior for entities. This leads to PickingBehavior having two purposes: mark an entity for use in a backend, and describe how it should be picked. Discussion led to the name Pickablemaking more sense (also: this is what the component was named before upstreaming).

A follow-up pass will be made after this PR to unify backends.

Solution

Replace all instances of PickingBehavior and picking_behavior with Pickable and pickable, respectively.

Testing

CI

Migration Guide

Change all instances of PickingBehavior to Pickable.

[alice-i-cecile]

I agree with this. Once the backends are unified in behavior, we should add docs to explain that Pickable is always required.

[aevyrie]

I agree with this. Once the backends are unified in behavior, we should add docs to explain that Pickable is always required

@alice-i-cecile is that correct? I thought we wanted both opt in and opt out? E.g. in opt-out, Pickable is not required.