convert TestWalkingChar to the new animation system

[stephengold]

This addresses another piece of issue #1452.

Once #1499 is fixed, we can replace

        ArmatureMask walkingMask = new ArmatureMask();
        walkingMask.addBones(armature, "head", "spine", "spinehigh");
        walkingMask.addFromJoint(armature, "hip.left");
        walkingMask.addFromJoint(armature, "hip.right");
        walkingMask.addFromJoint(armature, "uparm.left");

with something like

        ArmatureMask walkingMask = new ArmatureMask(armature)
                .remove(shootingMask);

[pavly-gerges]

Nice work , I have now a better idea of what's the ArmatureMask 🙂😁.