Support automatic lazy widget bundling

[rorticus]

Enhancement

When using @dojo/core/load to lazy load a module, we want automatically add the module to its own bundle

Given,

registry.define('my-widget', () => {
    return load(require, './MyWidget')
        .then(([ MyWidget ]) => MyWidget.default);
});

We want cli-build to add MyWidget to it's own bundle using something like,

require(`bundle-loader?lazy&name=${widgetName}!./Widget`);