Implement AsFd/AsRawFd for EventLoop<T>

This should help other crates to integrate winit's event loop into
their bigger event loop without adding an extra thread.

src/platform_impl/linux/x11/mod.rs

@@ -32,7 +32,7 @@ use std::{
     ops::Deref,
     os::{
         raw::*,
-        unix::io::{AsRawFd, BorrowedFd},
+        unix::io::{AsFd, AsRawFd, BorrowedFd, RawFd},
     },
     ptr,
     rc::Rc,
@@ -658,6 +658,18 @@ impl<T: 'static> EventLoop<T> {
     }
 }
 
+impl<T> AsFd for EventLoop<T> {
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        self.event_loop.as_fd()
+    }
+}
+
+impl<T> AsRawFd for EventLoop<T> {
+    fn as_raw_fd(&self) -> RawFd {
+        self.event_loop.as_raw_fd()
+    }
+}
+
 pub(crate) fn get_xtarget<T>(target: &RootELW<T>) -> &EventLoopWindowTarget<T> {
     match target.p {
         super::EventLoopWindowTarget::X(ref target) => target,