support web-workers for jpeg-8 color using built-in features 'createImageBitmap' and 'OffscreenCanvas' for enhanced performance

[Zaid-Safadi]

For JPEGBaseline8BitColor images the decoder currently uses the img element and HTML Canvas by converting binary image data to Base64 to support the decoding. https://github.com/cornerstonejs/cornerstoneWADOImageLoader/blob/master/src/imageLoader/decodeJPEGBaseline8BitColor.js#L30

This process:

1. Prevent using web-workers as DOM elements can't be used/created there
2. May suffer from performance issues when binary data is large and converting to base64

A better approach is using the new native JavaScript features 'createImageBitmap' and 'OffscreenCanvas' -when supported- to decode the image and run it in a web-worker:

1. OffscreenCanvas in web-wroker is will improve the performance as suggested by several posts such as: https://developers.google.com/web/updates/2018/08/offscreen-canvas
2. No need to convert the image binary data to base64 when using the createImageBitmap method
3. We can now take advantage of web-workers