Introduce explicit id field to Settings

... and use it to set the application id of the window on Unix systems, instead of relying on the title of the application.

winit/src/application.rs

@@ -152,6 +152,7 @@ where
             &application.title(),
             application.mode(),
             event_loop.primary_monitor(),
+            settings.id,
         )
         .with_menu(Some(conversion::menu(&application.menu())))
         .build(&event_loop)

winit/src/settings.rs

@@ -16,6 +16,12 @@ use winit::window::WindowBuilder;
 /// The settings of an application.
 #[derive(Debug, Clone, Default)]
 pub struct Settings<Flags> {
+    /// The identifier of the application.
+    ///
+    /// If provided, this identifier may be used to identify the application or
+    /// communicate with it through the windowing system.
+    pub id: Option<String>,
+
     /// The [`Window`] settings
     pub window: Window,
 
@@ -70,6 +76,7 @@ impl Window {
         title: &str,
         mode: Mode,
         primary_monitor: Option<MonitorHandle>,
+        _id: Option<String>,
     ) -> WindowBuilder {
         let mut window_builder = WindowBuilder::new();
 
@@ -112,7 +119,10 @@ impl Window {
         ))]
         {
             use ::winit::platform::unix::WindowBuilderExtUnix;
-            window_builder = window_builder.with_app_id(title.to_string());
+
+            if let Some(id) = _id {
+                window_builder = window_builder.with_app_id(id);
+            }
         }
 
         #[cfg(target_os = "windows")]
@@ -122,6 +132,7 @@ impl Window {
             if let Some(parent) = self.platform_specific.parent {
                 window_builder = window_builder.with_parent_window(parent);
             }
+
             window_builder = window_builder
                 .with_drag_and_drop(self.platform_specific.drag_and_drop);
         }