Masks in the Animation State Graph are not applied if the skeletal hierarchy is not a child of the entity that has the Anim component

Description

When applying a mask as part of an Animation State Graph Layer the mask is not properly applied if the skeletal hierarchy is not a direct child of the entity that the Anim component is on.

Demonstration project: https://playcanvas.com/project/1172859/overview/animation-masks-template-bug

Both of the characters are set up to loop a run cycle in the base layer, with a sword swinging animation masked onto the upper body. Only the one where the bone hierarchy is a child of the entity holding the Anim component works.

As this is how the entity hierarchy is defined automatically when you import a model, it requires us to remember to make a change after importing each new model.

Steps to Reproduce

1. Create a simple animation graph with two layers
2. Set up the entity as it would be on a normal import of the model:

3. Set the second layer as masked onto the base.
4. Observe that the mask is not applied.
5. Duplicate the entity and edit it so that the skeletal hierarchy is a child of the entity with the Anim component

6. Observe that the mask is correctly applied.

This restriction on entity hierarchy appears to be being enforced in components/anim/system.js in the cloneComponent function: The copying logic only occurs if you're either not specifying the rootbone, or if the rootbone is also the anim component entity.

cloneComponent(entity, clone) {
        let masks;
        // If the component animaites from the components entity, any layer mask hierarchy should be updated from the old entity to the cloned entity.
        if (!entity.anim.rootBone || entity.anim.rootBone === entity) {

(which appears to be part of a fix for an earlier issue with masks)