feat: Add will-resize event to TopLevelWindow (#13649)

The new `will-resize` event can be used to prevent the resize from
happening before the native window is actually resized. This is in
contrast to the existing the `resize` event, which is sent *after* the
native window has already been resized. For apps with e.g. custom window
snapping logic, the `resize` event is not sufficient because it will
result in flickering between the dragged size and the snapped size.

`will-resize` is only emitted on macOS and Windows.

atom/browser/ui/cocoa/atom_ns_window_delegate.mm

@@ -112,6 +112,15 @@
                extraHeightPlusFrame);
   }
 
+  {
+    bool prevent_default = false;
+    gfx::Rect new_bounds(gfx::Point(sender.frame.origin), gfx::Size(newSize));
+    shell_->NotifyWindowWillResize(new_bounds, &prevent_default);
+    if (prevent_default) {
+      return sender.frame.size;
+    }
+  }
+
   return newSize;
 }