Dynamic material support in Fabric

[lilleyse]

As of Kit 104.2 it's not possible to update material attributes (including textures) after the material is created or assign new materials to existing prims. So we are stuck with the originally assigned material and any sort of dynamic updates are not possible.

Currently our workaround is to destroy the existing prim whenever material changes happen, e.g. when higher res imagery is attached to the tile.

cesium-omniverse/src/core/src/FabricPrepareRenderResources.cpp

Lines 158 to 163 in 0b2499e

	if (pTileRenderResources->geomPaths.size() > 0) {
	// Already created the tile with lower-res imagery.
	// Due to Kit 104.2 material limitations, we can't update the texture or assign a new material to the prim.
	// But we can delete the existing prim and create a new prim.
	FabricStageUtil::removeTile(pTileRenderResources->allPrimPaths, pTileRenderResources->textureAssetNames);
	}

Once dynamic material updates are supported in Kit, it unlocks several improvements for us:

• No longer need to destroy prims when higher res imagery is attached to the tile
• Mesh and material pooling becomes possible
• Makes it easier to implement multiple raster overlays: Support for multiple raster overlays #84

CC #169