message: add requiresNormal accessor to PolyfaceData
diff: @@ -163,6 +163,7 @@ export class PolyfaceData {
  if (!NumberArray.isExactEqual(this.edgeVisible, other.edgeVisible)) return false;
  return true;
  }
  + public get requireNormals(): boolean { return undefined !== this.normal; }
  public get pointCount() { return this.point.length; }
  public get normalCount() { return this.normal ? this.normal.length : 0; }
  public get paramCount() { return this.param ? this.param.length : 0; }
  @@ -589,7 +590,6 @@ export abstract class PolyfaceVisitor extends PolyfaceData {
  public abstract currentReadIndex(): number;
  public abstract moveToNextFacet(): boolean;
  public abstract reset(): void;
  -
  public abstract clientPointIndex(i: number): number;
  public abstract clientParamIndex(i: number): number;
  public abstract clientNormalIndex(i: number): number;
  