Implement part of Berkeley Socket API for libc-wasi (#1036)

Refer to [Networking API design](https://github.com/WebAssembly/WASI/issues/370)
and [feat(socket): berkeley socket API v2](https://github.com/WebAssembly/WASI/pull/459):

- Support the socket API of synchronous mode, including `socket/bind/listen/accept/send/recv/close/shutdown`,
    the asynchronous mode isn't supported yet.
- Support adding `--addr-pool=<pool1,pool2,..>` argument for command line to identify the valid ip address range
- Add socket-api sample and update the document

core/shared/platform/common/posix/posix_socket.c

@@ -8,6 +8,16 @@
 
 #include <arpa/inet.h>
 
+static void
+textual_addr_to_sockaddr(const char *textual, int port, struct sockaddr_in *out)
+{
+    assert(textual);
+
+    out->sin_family = AF_INET;
+    out->sin_port = htons(port);
+    out->sin_addr.s_addr = inet_addr(textual);
+}
+
 int
 os_socket_create(bh_socket_t *sock, int tcp_or_udp)
 {
@@ -113,6 +123,23 @@ os_socket_accept(bh_socket_t server_sock, bh_socket_t *sock, void *addr,
     return BHT_OK;
 }
 
+int
+os_socket_connect(bh_socket_t socket, const char *addr, int port)
+{
+    struct sockaddr_in addr_in = { 0 };
+    socklen_t addr_len = sizeof(struct sockaddr_in);
+    int ret = 0;
+
+    textual_addr_to_sockaddr(addr, port, &addr_in);
+
+    ret = connect(socket, (struct sockaddr *)&addr_in, addr_len);
+    if (ret == -1) {
+        return BHT_ERROR;
+    }
+
+    return BHT_OK;
+}
+
 int
 os_socket_recv(bh_socket_t socket, void *buf, unsigned int len)
 {
@@ -138,3 +165,13 @@ os_socket_shutdown(bh_socket_t socket)
     shutdown(socket, O_RDWR);
     return BHT_OK;
 }
+
+int
+os_socket_inet_network(const char *cp, uint32 *out)
+{
+    if (!cp)
+        return BHT_ERROR;
+
+    *out = inet_network(cp);
+    return BHT_OK;
+}