Call terminate from Quit menu.

Unifies the closing logic between clicking on the icon menu Quit and the Quit menu.

native/Avalonia.Native/src/OSX/window.mm

@@ -1887,18 +1887,7 @@ NSArray* AllLoopModes = [NSArray arrayWithObjects: NSDefaultRunLoopMode, NSEvent
 
 +(void)closeAll
 {
-    NSArray<NSWindow*>* windows = [NSArray arrayWithArray:[NSApp windows]];
-    auto numWindows = [windows count];
-    
-    for(int i = 0; i < numWindows; i++)
-    {
-        auto window = (AvnWindow*)[windows objectAtIndex:i];
-        
-        if([window parentWindow] == nullptr) // Avalonia will handle the child windows.
-        {
-            [window performClose:nil];
-        }
-    }
+    [[NSApplication sharedApplication] terminate:self];
 }
 
 - (void)performClose:(id)sender