Async DNS resolution on Windows

[HertzDevil]

Resolves part of #13619.

Here is a very brief benchmark:

require "socket"
require "benchmark"

DOMAINS = %w(
  google.com
  crystal-lang.org
  stackoverflow.com
  llvm.org
)

def dns(domains, n)
  ch = Channel(Array(Socket::Addrinfo)?).new
  n.times do
    spawn do
      domains.each do |domain|
        ch.send(Socket::Addrinfo.tcp(domain, 80))
      rescue
        ch.send(nil)
      end
    end
  end
  (n * domains.size).times { ch.receive }
end

Benchmark.ips(calculation: 60.seconds, warmup: 10.seconds) do |b|
  b.report("good") { dns(DOMAINS, 1000) }
  b.report("bad") { dns(%w(badhostname), 5) }
end

good  11.26  ( 88.83ms) (±11.89%)  2.34MB/op        fastest
 bad 370.10m (  2.70s ) (± 0.44%)  10.4kB/op  30.42× slower

Without this PR:

good   1.82  (550.44ms) (±18.24%)  2.46MB/op        fastest
 bad  74.04m ( 13.51s ) (± 0.15%)  10.6kB/op  24.54× slower

[straight-shoota]

issue: GetAddrInfoExW only supports overlapped operations since Windows 8. Crystal technically supports down to Windows 7, although only with a flag (-Dwin7).
If we want to continue support for Windows 7, we would need to keep the getaddrinfo implementation or add a non-overlapped implementation for GetAddrInfoExW.

[Sija]

Could be simplified:

Suggested change

	if result == 0
	return addrinfos
	else
	case error = WinError.new(result.to_u32!)
	when .wsa_io_pending?
	# used in `Crystal::IOCP::OverlappedOperation#try_cancel_getaddrinfo`
	operation.handle = cancel_handle
	else
	raise ::Socket::Addrinfo::Error.from_os_error("GetAddrInfoExW", error, domain: domain, type: type, protocol: protocol, service: service)
	end
	end
	return addrinfos if result.zero?
	case error = WinError.new(result.to_u32!)
	when .wsa_io_pending?
	# used in `Crystal::IOCP::OverlappedOperation#try_cancel_getaddrinfo`
	operation.handle = cancel_handle
	else
	raise ::Socket::Addrinfo::Error.from_os_error("GetAddrInfoExW", error, domain: domain, type: type, protocol: protocol, service: service)
	end