Time scrubbing in the editor is hard to find and very fiddly

### Description

When testing longer animations, it would be nice to be able to scrub time in modelviewer.dev/editor. This exists (and is very useful) on https://sandbox.babylonjs.com/ but since there's differences in behaviour that's not always enough to test if a file works correctly in model-viewer.

Related
- https://github.com/mrdoob/three.js/issues/24018