asyncnet ssl overhaul (#24896)

Fixes #24895

- Remove all  bio handling
- Remove all `sendPendingSslData` which only seems to make things work
by chance
- Wrap the client socket on `acceptAddr` (std/net does this)
- Do the SSL handshake on accept (std/net does this)

The only concern is if addWrite/addRead works well on Windows.

(cherry picked from commit 8518cf079f)

tests/async/t24895.nim

@@ -0,0 +1,79 @@
+discard """
+  cmd: "nim $target --hints:on --define:ssl $options $file"
+"""
+
+{.define: ssl.}
+
+import std/[asyncdispatch, asyncnet, net, openssl]
+
+var port0: Port
+var checked = 0
+
+proc server {.async.} =
+  let sock = newAsyncSocket(AF_INET, SOCK_STREAM, IPPROTO_TCP, buffered = true)
+  doAssert sock != nil
+  defer: sock.close()
+  let sslCtx = newContext(
+    protSSLv23,
+    verifyMode = CVerifyNone,
+    certFile = "tests/testdata/mycert.pem",
+    keyFile = "tests/testdata/mycert.pem"
+  )
+  doAssert sslCtx != nil
+  defer: sslCtx.destroyContext()
+  wrapSocket(sslCtx, sock)
+  #sock.bindAddr(Port 8181)
+  sock.bindAddr()
+  port0 = getLocalAddr(sock)[1]
+  sock.listen()
+  echo "accept"
+  let clientSocket = await sock.accept()
+  defer: clientSocket.close()
+  wrapConnectedSocket(
+    sslCtx, clientSocket, handshakeAsServer, "localhost"
+  )
+  let sdata = "x" & newString(41)
+  let sfut = clientSocket.send(sdata)
+  let rdata = newString(42)
+  let rfut = clientSocket.recvInto(addr rdata[0], rdata.len)
+  echo "send"
+  await sfut
+  echo "recv"
+  let rLen = await rfut  # it hang here until the client closes the connection or sends more data
+  doAssert rLen == 42, $rLen
+  doAssert rdata[0] == 'x', $rdata[0]
+  echo "ok"
+  inc checked
+
+proc client {.async.} =
+  let sock = newAsyncSocket(AF_INET, SOCK_STREAM, IPPROTO_TCP, buffered = true)
+  doAssert sock != nil
+  defer: sock.close()
+  let sslCtx = newContext(
+    protSSLv23,
+    verifyMode = CVerifyNone
+  )
+  doAssert sslCtx != nil
+  defer: sslCtx.destroyContext()
+  wrapSocket(sslCtx, sock)
+  #await sock.connect("127.0.0.1", Port 8181)
+  await sock.connect("localhost", port0)
+  let sdata = "x" & newString(41)
+  echo "send"
+  await sock.send(sdata)
+  let rdata = newString(42)
+  echo "recv"
+  let rLen = await sock.recvInto(addr rdata[0], rdata.len)
+  doAssert rLen == 42, $rLen
+  doAssert rdata[0] == 'x', $rdata[0]
+  #await sleepAsync(10_000)
+  #await sock.send("x")
+  echo "ok"
+  inc checked
+
+discard getGlobalDispatcher()
+let serverFut = server()
+waitFor client()
+waitFor serverFut
+doAssert checked == 2
+doAssert not hasPendingOperations()