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.
- Improves op performance.
- Handle op-metadata (errors, promise IDs) explicitly in the op-layer vs
per op-encoding (aka: out-of-payload).
- Remove shared queue & custom "asyncHandlers", all async values are
returned in batches via js_recv_cb.
- The op-layer should be thought of as simple function calls with little
indirection or translation besides the conceptually straightforward
serde_v8 bijections.
- Preserve concepts of json/bin/min as semantic groups of their
inputs/outputs instead of their op-encoding strategy, preserving these
groups will also facilitate partial transitions over to v8 Fast API for the
"min" and "bin" groups
