feat: allow nesting non-component blocks inside components

The way components work in Builder is growing on me... I appreciate the idea that nested blocks within a component can have their properties overridden at any level individually in every iteration of that component.

What would make this all that much more useful would be the ability to nest non-component blocks inside any component object where that object supports children.

For example, we could create a default content container as a div with a max width, padding, etc, and then use that "Container" component every time we need to contain content at a consistent width throughout the site. This could provide a functional alternative to global classes, where any further design updates could be assigned to the component and would push out across the site from there.