[Video module]: Use Offscreen Canvas instead of Offscreen Framebuffer

this is an attempt, in trying to use emscripten to render in an offscreen canvas from a pthread. But this does not work.

A possible workaround would be to add bitmaprenderer support, to avoid having to transfer control to a pthread.

UI:

<canvas id="canvas"></canvas>
<script>
    var bitmapcontext = document.getElementById("canvas").getContext("bitmaprenderer");
    var worker = new Worker("./worker.js");
    worker.onmessage = function (evt) {
        var bitmap = evt.data.bitmap;
        bitmapcontext.transferFromImageBitmap(bitmap);
    };
</script>

worker