Create an initial build theme command that encapsulates the existing build tooling used by @dojo/themes.

The resulting output should contain:

• All assets (fonts, icons, etc.) included in the theme src
• The raw .m.css files so that composition is still possible (e.g., composes: root from 'my-theme/my-widget.m.css';)
• index.js and index.css files that contain the transformed CSS classes
• hashed JS and CSS equivalents of index.js and index.css for use with custom elements (the JS file should also register the theme with window.dojoce)