Allow Usage Of Scale Factor For Non-Static Canvas

[lsh]

The View API only allows for a scaleFactor for static images. However sometimes rendering at a larger logical size in the browser is useful. Currently in the renderer, if the Canvas is being rendered in the DOM, the scaleFactor is defined as the devicePixelRatio.

A solution is to add an options.scaleFactor parameter to the View constructor (defaults to devicePixelRatio) and use it in the CanvasRenderer.

[kanitw]

cc: @jheer any opinion here?