Add app id setting for linux

winit/src/settings/linux.rs

@@ -0,0 +1,11 @@
+//! Platform specific settings for Linux.
+
+/// The platform specific window settings of an application.
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
+pub struct PlatformSpecific {
+    /// Sets the application id of the window.
+    ///
+    /// As a best practice, it is suggested to select an application id that match
+    /// the basename of the application’s .desktop file.
+    pub application_id: String,
+}