This commit aligns `Headers` to spec. It also removes the now unused
03_dom_iterable.js file. We now pass all relevant `Headers` WPT. We do
not implement any sort of header filtering, as we are a server side
runtime.
This is likely not the most efficient implementation of `Headers` yet.
It is however spec compliant. Once all the APIs in the `HTTP` hot loop
are correct we can start optimizing them. It is likely that this commit
reduces bench throughput temporarily.
This commit starts splitting out the deno_web op crate into multiple
smaller crates. This commit splits out WebIDL and URL API, but in the
future I want to split out each spec into its own crate. That means we
will have (in rough order of loading): `webidl`, `dom`, `streams`,
`console`, `encoding`, `url`, `file`, `fetch`, `websocket`, and
`webgpu` crates.
