Pass in importOptions to GLTFParser, copy ior in PhysicalMaterial.setValues, add isDRACOLoader2

src/assetmanager/import/DRACOLoader2.ts

 export class DRACOLoader2 extends DRACOLoader implements ILoader<BufferGeometry, Mesh|undefined> {
     public encoderPending: Promise<any>|null = null
     public encoderConfig: any = {type: 'js'}
+    readonly isDRACOLoader2 = true
 
     public static DRACO_LIBRARY_PATH = 'https://cdn.jsdelivr.net/gh/google/draco@1.5.6/javascript/' // https://github.com/google/draco
     // public static DRACO_LIBRARY_PATH = 'https://www.gstatic.com/draco/versioned/decoders/1.4.1/'

src/assetmanager/import/GLTFLoader2.ts

     // loads the viewer config and handles loading the draco loader for extension
     gltfViewerParser = (viewer: ThreeViewer): (p: GLTFParser)=>GLTFLoaderPlugin => {
         return (parser: GLTFParser) => {
+            parser.importOptions = this.importOptions || undefined
             const getDependency = parser.getDependency
             parser.getDependency = async(type: string, index: number) => {
                 const res = await getDependency.call(parser, type, index)
         parent.children.splice(index, 0, line2)
     }
 }
+
+declare module 'three/examples/jsm/loaders/GLTFLoader.js'{
+    export interface GLTFParser {
+        importOptions?: ImportAddOptions
+        // getDependency(type: string, index: number): Promise<Object3D|Texture|Line|LineSegments|LineLoop>
+    }
+}

src/core/material/PhysicalMaterial.ts

 
         if (clearCurrentUserData === undefined) clearCurrentUserData = (<Material>parameters).isMaterial
         if (clearCurrentUserData) this.userData = {}
+
+        if ((parameters as any).ior !== undefined) this.ior = (parameters as any).ior // ior is not serialized in MeshPhysicalMaterial.toJSON, so we need to set it here
         iMaterialCommons.setValues(super.setValues).call(this, parameters)
 
         if (!isFinite(this.attenuationDistance)) this.attenuationDistance = 0 // hack for ui