Compare behavior of Context2d and WebGL drawers

Context2d drawer (default in OSD <= 4.1.0)

New WebGL drawer

Image options (drag and drop to re-order images)

HTMLDrawer: legacy pre-HTML5 drawer that uses <img> elements for tiles

HTML-based rendering can be selected in two different ways: 
    // via the 'html' drawer option:
    let viewer = OpenSeadragon({
        ...
        drawer: 'html',
        ...
    });

    // or by passing the HTMLDrawer constructor
    let viewer = OpenSeadragon({
        ...
        drawer:OpenSeadragon.HTMLDrawer,
        ...
    });