[io-layer] Extract socket (#4241)

[io-layer] Extract socket (#4241)

* [socket] Extract win32 and unix specific code from w32socket.c

* [socket] Extract WSAGetLastError and WSASetLastError

* [socket] Extract closesocket

* [socket] Extract iocltsocket

* [socket] Extract socket-wrappers.h functions

* [socket] Extract w32handle operations

* [socket] Extract WSAIoctl

* [socket] Do not use mono_w32socket_ioctl for disconnect

* [socket] Extract errno_to_WSA

* [socket] Remove redundant mono_w32handle_get_type/mono_w32handle_lookup

* [socket] Inline _wapi_* functions

* [socket] Make disconnect not rely on mono_w32socket_ioctl

* [socket] Remove unused parameters to mono_w32socket_transmit_file

* [socket] Refactor calls to mono_w32socket_convert_error

* [socket] Remove dead code