eframe: read the state of native window's input focus and request it (#2900)

* Add ability to read the native window's focus state

* Add `eframe::Frame::focus()` for requesting the native window's focus

* rename the output field `active` → `focused` for consistency

crates/eframe/src/epi.rs

@@ -814,6 +814,15 @@ impl Frame {
         self.output.minimized = Some(minimized);
     }
 
+    /// Bring the window into focus (native only). Has no effect on Wayland, or if the window is minimized or invisible.
+    ///
+    /// This method puts the window on top of other applications and takes input focus away from them,
+    /// which, if unexpected, will disturb the user.
+    #[cfg(not(target_arch = "wasm32"))]
+    pub fn focus(&mut self) {
+        self.output.focus = Some(true);
+    }
+
     /// Maximize or unmaximize window. (native only)
     #[cfg(not(target_arch = "wasm32"))]
     pub fn set_maximized(&mut self, maximized: bool) {
@@ -938,6 +947,9 @@ pub struct WindowInfo {
     /// Are we maximized?
     pub maximized: bool,
 
+    /// Is the window focused and able to receive input?
+    pub focused: bool,
+
     /// Window inner size in egui points (logical pixels).
     pub size: egui::Vec2,
 
@@ -1129,6 +1141,10 @@ pub(crate) mod backend {
         #[cfg(not(target_arch = "wasm32"))]
         pub maximized: Option<bool>,
 
+        /// Set to some bool to focus window.
+        #[cfg(not(target_arch = "wasm32"))]
+        pub focus: Option<bool>,
+
         #[cfg(not(target_arch = "wasm32"))]
         pub screenshot_requested: bool,
     }