Option for automatically parsing metadata

[lourot]

In order to populate data-image-regions=, if parsing image metadata on the front-end is good enough, one has to write a bit of boilerplate at the moment, as shown in the CodeSandbox:

        const imgElement = document.getElementById("skater");
        const image = await fetch(imgElement.src);
        const arrayBuffer = await image.arrayBuffer();
        const buffer = Buffer.Buffer.from(arrayBuffer);
        const parser = new ImageDisplayControl.Parser(buffer);
        const regions = parser.getIdcMetadata("rectangle", "crop");
        imgElement.dataset.imageRegions = JSON.stringify(regions);

It would be nice to be able to pass a flag to the web-component telling it to do this for us, if ImageDisplayControl.Parser exists, i.e. if https://github.com/Frameright/image-display-control-metadata-parser has been loaded.

Possible optimization / strech goal

We could then store the parsed metadata in the localstorage in order not to have to parse it again. We need to find a cheap way though to determine when what we have cached is stale.