…essed responses

CI hung in 'http server compresses and flushes each chunk of a streamed
resource' on every platform: with content-encoding now preserved on
decompressed fetch responses, proxying a Response straight into
respondWith()/Deno.serve forwarded content-encoding, content-length and
transfer-encoding describing the original wire body together with the
already-decoded body. The server then skipped its own compression
(content-encoding present), so clients received plain bytes labeled as
compressed and the test's DecompressionStream never produced output.

Keep the headers visible on the Response per the fetch spec, but mark
responses whose body was transparently decompressed (extensions marker
in Rust, bodyDecoded on the inner response in JS) and strip the three
wire-framing headers at re-serialization boundaries: Deno.serve, the
legacy serveHttp respondWith, and Cache API storage.

Adds a regression test proxying a decompressed fetch response through
Deno.serve, verified to fail without this change.

…oding

# Conflicts:
#	ext/http/00_serve.ts