Implement sock_accept

With the addition of `sock_accept()` in `wasi-0.11.0`, wasmtime can now
implement basic networking for pre-opened sockets.

For Windows `AsHandle` was replaced with `AsRawHandleOrSocket` to cope
with the duality of Handles and Sockets.

For Unix a `wasi_cap_std_sync::net::Socket` enum was created to handle
the {Tcp,Unix}{Listener,Stream} more efficiently in
`WasiCtxBuilder::preopened_socket()`.

The addition of that many `WasiFile` implementors was mainly necessary,
because of the difference in the `num_ready_bytes()` function.

A known issue is Windows now busy polling on sockets, because except
for `stdin`, nothing is querying the status of windows handles/sockets.

Another know issue on Windows, is that there is no crate providing
support for `fcntl(fd, F_GETFL, 0)` on a socket.

Signed-off-by: Harald Hoyer <harald@profian.com>

crates/wasi-common/src/pipe.rs

@@ -189,6 +189,10 @@ impl<R: Read + Any + Send + Sync> WasiFile for ReadPipe<R> {
     async fn writable(&self) -> Result<(), Error> {
         Err(Error::badf())
     }
+
+    async fn sock_accept(&mut self, fdflags: FdFlags) -> Result<Box<dyn WasiFile>, Error> {
+        Err(Error::badf())
+    }
 }
 
 /// A virtual pipe write end.
@@ -348,4 +352,8 @@ impl<W: Write + Any + Send + Sync> WasiFile for WritePipe<W> {
     async fn writable(&self) -> Result<(), Error> {
         Err(Error::badf())
     }
+
+    async fn sock_accept(&mut self, fdflags: FdFlags) -> Result<Box<dyn WasiFile>, Error> {
+        Err(Error::badf())
+    }
 }