linux/x11: Restore differentiation of mouse/keyboard focus (#13995)

This restores https://github.com/zed-industries/zed/pull/13943 which was
reverted in #13974 because it was possible to get in a state where focus
could not be restored on a window.

In this PR there's an additional change: `FocusIn` and `FocusOut` events
are always handled, even if the `event.mode` is not "NORMAL". In my
testing, `alt-tabbing` between windows didn't produce `FocusIn` and
`FocusOut` events when we had that check. Now, with the check removed,
it's possible to switch focus between two windows again with `alt-tab`.


Release Notes:

- N/A

---------

Co-authored-by: Conrad <conrad@zed.dev>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/gpui/src/platform/test/window.rs

@@ -23,6 +23,7 @@ pub(crate) struct TestWindowState {
     pub(crate) should_close_handler: Option<Box<dyn FnMut() -> bool>>,
     input_callback: Option<Box<dyn FnMut(PlatformInput) -> DispatchEventResult>>,
     active_status_change_callback: Option<Box<dyn FnMut(bool)>>,
+    hover_status_change_callback: Option<Box<dyn FnMut(bool)>>,
     resize_callback: Option<Box<dyn FnMut(Size<Pixels>, f32)>>,
     moved_callback: Option<Box<dyn FnMut()>>,
     input_handler: Option<PlatformInputHandler>,
@@ -66,6 +67,7 @@ impl TestWindow {
             should_close_handler: None,
             input_callback: None,
             active_status_change_callback: None,
+            hover_status_change_callback: None,
             resize_callback: None,
             moved_callback: None,
             input_handler: None,
@@ -182,6 +184,10 @@ impl PlatformWindow for TestWindow {
         false
     }
 
+    fn is_hovered(&self) -> bool {
+        false
+    }
+
     fn set_title(&mut self, title: &str) {
         self.0.lock().title = Some(title.to_owned());
     }
@@ -225,6 +231,10 @@ impl PlatformWindow for TestWindow {
         self.0.lock().active_status_change_callback = Some(callback)
     }
 
+    fn on_hover_status_change(&self, callback: Box<dyn FnMut(bool)>) {
+        self.0.lock().hover_status_change_callback = Some(callback)
+    }
+
     fn on_resize(&self, callback: Box<dyn FnMut(Size<Pixels>, f32)>) {
         self.0.lock().resize_callback = Some(callback)
     }