Add simple wasm example using web worker and vtkAlgorithm abort

- This example has a simple `main` function which sets up the VTK
  pipeline using vtkTableBasedClipDataSet.
- It shows how one might leverage the vtkAlgorithm abort functionality
  because now all the VTK rendering and processing is offloaded into a
  web worker leaving the main thread free to go and set the abort flag.
- In this example, the abort flag is set whenever user mouses
  down and moves the cursor on the canvas. As soon as the mouse is
  released, the abort flag is reset.