Optimization - use willReadFrequently when initializing canvas

[ymoran00]

Chrome provides this warning:

Canvas2D: Multiple readback operations using getImageData are faster with the willReadFrequently attribute set to true. See: https://html.spec.whatwg.org/multipage/canvas.html#concept-canvas-will-read-frequently

So adding it may optimize the canvas for some browsers.

[getify]

For reference, here's the line that needs the change:

https://github.com/nimiq/qr-scanner/blob/abcfe1bce2703721408d8ce7ebde94a359998506/src/qr-scanner.ts#L980

that options object needs willReadFrequently: true added to it.