Manager::startAllHiding: don't treat fading in notifications specially

Previously, `Window::Notifications::Default::Manager` would not start
hiding notifications that are fading in when other notifications should
hide. This would lead to some notifications never hiding, e.g., when the
cursor passes through the notification too quickly and there was not
enough time for the notification to fade in completely.

Also renamed `Widget::isShowing` -> `Widget::isFadingIn` for clarity.

Fixes telegramdesktop#28811.

Telegram/SourceFiles/window/notifications_manager_default.cpp

@@ -188,16 +188,10 @@ void Manager::checkLastInput() {
 
 void Manager::startAllHiding() {
 	if (!hasReplyingNotification()) {
-		int notHidingCount = 0;
 		for (const auto &notification : _notifications) {
-			if (notification->isShowing()) {
-				++notHidingCount;
-			} else {
-				notification->startHiding();
-			}
+			notification->startHiding();
 		}
-		notHidingCount += _queuedNotifications.size();
-		if (_hideAll && notHidingCount < 2) {
+		if (_hideAll && _queuedNotifications.size() < 2) {
 			_hideAll->startHiding();
 		}
 	}

Telegram/SourceFiles/window/notifications_manager_default.h

@@ -143,7 +143,7 @@ class Widget : public Ui::RpWidget {
 		int shift,
 		Direction shiftDirection);
 
-	bool isShowing() const {
+	bool isFadingIn() const {
 		return _a_opacity.animating() && !_hiding;
 	}