Add api to get inner WatchDescriptor id, to work with c code. (#2718)

* Add api to get inner WatchDescriptor id, to work with c code.

* changelog

* rename WatchDescriptor::inner_id to as_raw

Author: navneetankur

changelog/2718.added.md

@@ -0,0 +1 @@
+Add WatchDescriptor::as_raw, to get libc id of WatchDescriptor.

src/sys/inotify.rs

@@ -113,6 +113,12 @@ pub struct Inotify {
 pub struct WatchDescriptor {
     wd: i32,
 }
+impl WatchDescriptor {
+    /// Raw WatchDescriptor, from libc.
+    pub fn as_raw(self) -> i32 {
+        self.wd
+    }
+}
 
 /// A single inotify event.
 ///
@@ -270,4 +276,4 @@ impl From<Inotify> for OwnedFd {
     fn from(value: Inotify) -> Self {
         value.fd
     }
-}
+}