7d7648f7ed
This enables two workflows: 1) Users that parsed some other format into MjSpec, or built it programmatically can export animated USD easily with as minimal as possible interaction with USD. 2) Creating a spec from USD, then modifying the spec, should not cause a duplication of data when writing to USD. PiperOrigin-RevId: 827627520 Change-Id: I02c8c14a18569547710e54f3704d52ac0bf70ce6