Add methods to get the position of a window's client area, relative to the desktop (#430)

* Add get_inner_position for windows, prototypes for other platforms

* Fix linux builds

* Implement get_inner_position for osx

* Add get_inner_pos implementations for other platforms

* Fixed get_inner_position on macOS

* Corrected set_position on macOS

* Added CHANGELOG entry

src/platform/linux/mod.rs

@@ -162,6 +162,14 @@ impl Window {
         }
     }
 
+    #[inline]
+    pub fn get_inner_position(&self) -> Option<(i32, i32)> {
+        match self {
+            &Window::X(ref m) => m.get_inner_position(),
+            &Window::Wayland(ref m) => m.get_inner_position(),
+        }
+    }
+
     #[inline]
     pub fn set_position(&self, x: i32, y: i32) {
         match self {

src/platform/linux/wayland/window.rs

@@ -113,6 +113,12 @@ impl Window {
         None
     }
 
+    #[inline]
+    pub fn get_inner_position(&self) -> Option<(i32, i32)> {
+        // Not possible with wayland
+        None
+    }
+
     #[inline]
     pub fn set_position(&self, _x: i32, _y: i32) {
         // Not possible with wayland

src/platform/linux/x11/window.rs

@@ -919,6 +919,11 @@ impl Window2 {
         self.get_geometry().map(|geo| geo.get_position())
     }
 
+    #[inline]
+    pub fn get_inner_position(&self) -> Option<(i32, i32)> {
+        self.get_geometry().map(|geo| geo.get_inner_position())
+    }
+
     pub fn set_position(&self, mut x: i32, mut y: i32) {
         if let Some(ref wm_name) = self.wm_name {
             // There are a few WMs that set client area position rather than window position, so