Use createImageBitmap for image decoding when available

[puckey]

While profiling in Chrome, I noticed quite a few ms being spent in decoding satellite images on the main thread. Using ImageBitmap this decoding could be offloaded to the background. ImageBitmap is currently supported by Firefox, Chrome & Opera.

https://developers.google.com/web/updates/2016/03/createimagebitmap-in-chrome-50

"The problem with decoding images is that it can be CPU intensive, and that can sometimes mean jank or checkerboarding. As of Chrome 50 (and in Firefox 42+) you now have another option: createImageBitmap(). It allows you to decode an image in the background, and get access to a new ImageBitmap primitive, which you can draw into a canvas in the same way you would an element, another canvas, or a video."

[puckey]

I created the following pull request for this: #6625

It contains one TODO: I am not completely sure what to do with the crossOrigin parameter passed to Resource._Implementations.createImage...

[pjcozzi]

Resources from #5963

• ImageBitmapLoader: Support Firefox's partial createImageBitmap implementation. mrdoob/three.js#12456
• https://twitter.com/donrmccurdy/status/925800420101931008
• https://twitter.com/superhoge/status/1052609244824887296

[mramato]

Implemented in #7579