DEV: Correctly render data- attributes in widget hbs templates (PR #10376)

In virtualdom, element ‘properties’ are not completely synonymous with element ‘attributes’. In particular, data- properties will not be rendered as attributes. To ensure all attributes are passed through, we need to include them under an attributes key. For more info, see https://github.com/Matt-Esch/virtual-dom/blob/master/docs/vnode.md#custom-attributes-data-

GitHub

Seems good!