Spec and implement improved UI/UX for refreshing and reloading tilesets and raster overlays

[corybarr]

Currently, some edits to raster overlays, cartographic polygons, etc, can result in a cascade of overloads. Starting from a product level, we should revisit the UX/UI with an eye out for the following:

• Avoiding tileset reloads
• Avoiding unused data request to external data sources
• If and when a user should request tileset and raster-overlay refreshes
• Potential debouncing techniques

Cesium for Unreal currently has some different approaches than Cesium for Omniverse. Listing these differences and deciding if they should be adopted provides a starting point.

[lilleyse]

One idea for cutting down on tileset reloads is to hardcode a maximum number of raster overlays per tile so that the material doesn't need to be recreated each time a new raster overlay is added or removed.

[corybarr]

I also wonder how feasible it is to add the visibility-toggle eye icon that USD prims have for each raster overlay. Changes to non-visible raster overlays could be batched until visible. Aside from being a way to disable reload, it also might make data exploration like comparison between raster-overlay datasets easier.