eglfs: Fix mouse events not being delivered to the frontmost window

Since QPlatformScreen::topLevelAt() wasn't implemented it would just fallback
to use QGuiApplication's window list.

Possibly fixes any other bug that relied on QApplication::topLevelAt().

The fix is to consult the compositor, which has proper z-order information,
unlike QGuiApplicationPrivate::window_list.

Task-Id: QTBUG-105256
Change-Id: I4202dd5d87e41b69c461c808d29b809af5b52d09
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
(cherry picked from commit 40d781b7b5e7925e4559cd725ddbfef307d5f455)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/plugins/platforms/eglfs/api/qeglfsscreen.cpp

@@ -212,4 +212,22 @@ QPixmap QEglFSScreen::grabWindow(WId wid, int x, int y, int width, int height) c
     return QPixmap();
 }
 
+QWindow *QEglFSScreen::topLevelAt(const QPoint &point) const
+{
+#ifndef QT_NO_OPENGL
+    QOpenGLCompositor *compositor = QOpenGLCompositor::instance();
+    const QList<QOpenGLCompositorWindow *> windows = compositor->windows();
+    const int windowCount = windows.size();
+
+    // Higher z-order is at the end of the list
+    for (int i = windowCount - 1; i >= 0; i--) {
+        QWindow *window = windows[i]->sourceWindow();
+        if (window->isVisible() && window->geometry().contains(point))
+            return window;
+    }
+#endif
+
+    return QPlatformScreen::topLevelAt(point);
+}
+
 QT_END_NAMESPACE

src/plugins/platforms/eglfs/api/qeglfsscreen_p.h

@@ -54,6 +54,8 @@ public:
 
     void handleCursorMove(const QPoint &pos);
 
+    QWindow *topLevelAt(const QPoint &point) const override;
+
 private:
     void setPrimarySurface(EGLSurface surface);