isEnabled = function (context)
    {
        return (prefix !== null) ? context[prefix] : null;
    }
Returns `true` if the given context has image smoothing enabled, otherwise returns `false`.
Returns null if no smoothing prefix is available.

@function Phaser.Display.Canvas.Smoothing.isEnabled
@since 3.0.0

@param {(CanvasRenderingContext2D|WebGLRenderingContext)} context - The context to check.

@return {?boolean} `true` if smoothing is enabled on the context, otherwise `false`. `null` if not supported.