Fix HttpClient-from-HttpService wrapper prematurely cancelling service promise.

This reverts the core change from: https://github.com/capnproto/capnproto/commit/6e4c5ce3c9f31a5e79b50cd9eaae6d03106edf98

There are a few reasons to believe that change was wrong:
- It meant that a pump would always throw and catch a DISCONNECTED exception, which violates the rule that we don't throw exceptions in "normal" operation.
- It could lead to trouble when combined with the previous commit, which could delay WebSocket disconnect until the service "completes" -- which would lead to a hang.

The commit message where I introduced this said something about bad behavior on OSX. We should address that directly, if it is still a problem.

The client app will typically discard the returned response body upon reading EOF. However, the server app may not actually be "done" with the service callback yet at this point. Usually it completes very soon after, but it may need another turn or two of the event loop. If the client discards the response body stream, the server-side promise is discarded, cancelling whatever was left. This is awkward, so we should instead delay the client from seeing EOF until the server has actually finished up.

Log more info in VectorOutputStream::write() KJ_REQUIRE

This seems to be the case, for example, on WSL.

Detect EOF in copyChunk

This is to help debug an issue in Cloudflare Workers. I also added the same debug info to the ArrayOutputStream case, mostly for pleasing symmetry.

If holes are not supported on the target system and size to `copy` was passed as `kj::maxValue()`, this could lead to near-infinite loops.

Fix cancellation in AsyncTee::PumpSink.

Typo in c++/src/kj/array.h

Fix overflow in PackedInputStream.

Multi-host HttpClient shouldn't rewrite URL.

Fix typo

Extend kj::Url with option to not collapse empty path/query components.

Add `group` to the list of possible annotations targets.

initialize anonymous enums in isPlausiblyText() and isPlausiblyJson()

This is to fix a complaint about Cloudflare Workers removing these components as requests pass through, which apparently breaks someone's funky URLs.

Arguably "." and ".." processing presents a similar problems. But, allowing ".." to pass through is much more likely to lead to security problems. Browsers will generally process "." and ".." before sending a request (whereas they won't collapse double-slashes), so we're following their lead here.

Allow WebSocket to keep sending after close().

In Cloudflare Workers, we've observed applications in the wild that continue to send messages after a Close message. This is incorrect, but it happens, and we end up logging a spurious error as we attempt to proxy the message through.

By removing this restriction, we can now proxy these WebSockets despite the incorrect usage.

Make KJ_CASE_ONEOF work in templated contexts.

Don't escape forward slashes in JSON output

Forward slashes don't need to be escaped in JSON.

Merge pull request #751 from capnproto/harris/zero-length-responses-get-no-content-length-and-great-sadness

Zero-length HTTP responses get no Content-Length header

There is currently no way to explicitly omit a Content-Length/Transfer-Encoding header on an HTTP response to a HEAD request. This is awkward for a proxy, which would ideally pass along responses as-is, even if they have no such headers.

This change allows an author to pass zero as the expected body length to HttpService::Response::send() to mean "do not set any body header." This means that a proxy might strip Content-Length: 0 headers, but will never add a Content-Length header where there was none before.

Silence compiler warning

Implement JSON-RPC adapter to Cap'n Proto interfaces.

This isn't related to JSON-RPC but is a fix needed for the Ekam language server.

This implements JSON-RPC 2.0: https://www.jsonrpc.org/specification