Prevent dynamic geometry update if time hasn't change

[mpnewcomb]

I have a 8 Polyline Entities. I'm not quite sure how many points, but probably quite a few because there are curves approximated by lines. Cesium was extremely sluggish while zooming in/out and panning around. Profiled the app and rendering is taking 250ms. I look further and see Clock.tick... I'm not advancing time, but still this is being called... look further and see Viewer_onTick->DataSourceDisplay.update->PolylineVisualizer.update->DynamicGeometryBatch.update->DynamicGeometryUpdater.update and watch as it basically destroys all my polylines... only for Scene.render to recreate them!? And, time has not changed!

Somewhere along that chain, somebody needs to check to see if time has actually changed before doing all that work.

[emackey]

This is a subset of a larger issue #2310. Probably worth doing this as low-hanging fruit, but the deeper problem is more involved.