Add workaround for macOS leaveEvent() bugs.

On macOS sometimes when mouse leaves the window we don't receive leaveEvent()
calls in the nested widgets, like buttons, only for the window itself.

Telegram/SourceFiles/window/main_window.h

@@ -20,6 +20,7 @@ Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
 */
 #pragma once
 
+#include <rpl/event_stream.h>
 #include "window/window_title.h"
 #include "base/timer.h"
 
@@ -96,6 +97,8 @@ public:
 		return _dragFinished;
 	}
 
+	rpl::producer<> leaveEvents() const;
+
 public slots:
 	bool minimizeToTray();
 	void updateGlobalMenu() {
@@ -104,6 +107,7 @@ public slots:
 
 protected:
 	void resizeEvent(QResizeEvent *e) override;
+	void leaveEvent(QEvent *e) override;
 
 	void savePosition(Qt::WindowState state = Qt::WindowActive);
 	void handleStateChanged(Qt::WindowState state);
@@ -187,6 +191,7 @@ private:
 	base::Timer _inactivePressTimer;
 
 	base::Observable<void> _dragFinished;
+	rpl::event_stream<> _leaveEvents;
 
 };