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/cap-std-sync/src/file.rs

@@ -25,6 +25,9 @@ impl WasiFile for File {
     fn as_any(&self) -> &dyn Any {
         self
     }
+    async fn sock_accept(&mut self, _fdflags: FdFlags) -> Result<Box<dyn WasiFile>, Error> {
+        Err(Error::badf())
+    }
     async fn datasync(&self) -> Result<(), Error> {
         self.0.sync_data()?;
         Ok(())
@@ -171,8 +174,19 @@ impl AsHandle for File {
     }
 }
 
+#[cfg(windows)]
+use io_extras::os::windows::{AsRawHandleOrSocket, RawHandleOrSocket};
+#[cfg(windows)]
+impl AsRawHandleOrSocket for File {
+    #[inline]
+    fn as_raw_handle_or_socket(&self) -> RawHandleOrSocket {
+        self.0.as_raw_handle_or_socket()
+    }
+}
+
 #[cfg(unix)]
 use io_lifetimes::{AsFd, BorrowedFd};
+
 #[cfg(unix)]
 impl AsFd for File {
     fn as_fd(&self) -> BorrowedFd<'_> {