Implement dial, support IPv6 in httpclient (#5763)

* Implement dial, support IPv6 in httpclient

Added ``dial`` procedure to networking modules: ``net``, ``asyncdispatch``,
``asyncnet``. It merges socket creation, address resolution, and connection
into single step. When using ``dial``, you don't have to worry about
IPv4 vs IPv6 problem.

Fixed addrInfo loop in connect to behave properly.
Previously it would stop on first non-immediate failure, instead of
continuing and trying the remaining addresses.

Fixed newAsyncNativeSocket to raise proper error if socket creation
fails.

Fixes: #3811

* Check domain during connect() only on non-Windows

This is how it was in the previous implementation of connect().

* Call 'osLastError' before 'close' in net.dial

* Record osLastError before freeAddrInfo in net.dial

* Add missing docs for 'dial' proc

* Optimize dial to create one FD per domain, add tests

And make async IPv6 servers work on Windows.

* Add IPv6 test to uri module

* Fix getAddrString error handling

tests/async/tasyncdial.nim

@@ -0,0 +1,53 @@
+discard """
+  file: "tasyncdial.nim"
+  output: '''
+OK AF_INET
+OK AF_INET6
+'''
+"""
+
+import
+  nativesockets, os, asyncdispatch
+
+proc setupServerSocket(hostname: string, port: Port, domain: Domain): AsyncFD =
+  ## Creates a socket, binds it to the specified address, and starts listening for connecitons.
+  ## Registers the descriptor with the dispatcher of the current thread
+  ## Raises OSError in case of an error.
+  let fd = newNativeSocket(domain)
+  setSockOptInt(fd, SOL_SOCKET, SO_REUSEADDR, 1)
+  var aiList = getAddrInfo(hostname, port, domain)
+  if bindAddr(fd, aiList.ai_addr, aiList.ai_addrlen.Socklen) < 0'i32:
+    freeAddrInfo(aiList)
+    raiseOSError(osLastError())
+  freeAddrInfo(aiList)
+  if listen(fd) != 0:
+    raiseOSError(osLastError())
+  setBlocking(fd, false)
+  result = fd.AsyncFD
+  register(result)
+
+proc doTest(domain: static[Domain]) {.async.} =
+  const
+    testHost = when domain == Domain.AF_INET6: "::1" else: "127.0.0.1"
+    testPort = Port(17384)
+  let serverFd = setupServerSocket(testHost, testPort, domain)
+  let acceptFut = serverFd.accept()
+  let clientFdFut = dial(testHost, testPort)
+
+  let serverClientFd = await acceptFut
+  serverFd.closeSocket()
+
+  let clientFd = await clientFdFut
+
+  let recvFut = serverClientFd.recv(2)
+  await clientFd.send("Hi")
+  let msg = await recvFut
+
+  serverClientFd.closeSocket()
+  clientFd.closeSocket()
+
+  if msg == "Hi":
+    echo "OK ", domain
+
+waitFor(doTest(Domain.AF_INET))
+waitFor(doTest(Domain.AF_INET6))