Boilerplate generation

One of the trickiest parts of a ComponentizeJS workflow is figuring out the write structure to author the code to.

We should generate the boilerplate outline for the world being targetted as a new `generateBoilerplate` operation, which could become something like `jco componentize-gen world.wit` for example.

I've posted https://github.com/bytecodealliance/jco/issues/152 in jco for the bindgen discussion on this.