Toolbar menus open "without touching" the toolbar edge in dual monitor setup - Gnome wayland

[rickytower]

Affects versions :

• OS: Fedora Linux 35.20211207.0 (Silverblue)
• (Linux only) Desktop environment: Gnome-Wayland
• libgtk 3.24.30
• Version of Xournal++: 1.1.0
• commit git: 9d1277d-dirty
• Installation method: Flatpak (from flathub)

Describe the bug
I'm using dual monitor setup as in this picture below.

Dragging down the miniature of the second monitor in gnome-settings and applying that configuration causes the menus of the toolbar (such as the one to take an rectangular area) to open detached from the edge.

The external monitor has a 1920x1080 fullscreen resolution.

To Reproduce
Steps to reproduce the behavior:

1. Connect your computer to an external monitor
2. Open gnome settings > Displays and move away the miniature of the second screen from the upper edge.
3. Apply changes and open xournalpp. Try to open the submenus of the toolbar (the pencil, the rubber, the tool to move areas, etc..)

Here's a video that shows better the issue: https://youtu.be/m5cYb029Eow

Expected behavior
xournalpp should behave as in the first picture even if the display configuration is changed as shown in the second picture.

[bhennion]

I think it is due to our wcustom widget GtkMenuToolToggleButton. This should be fixed by #5154 (that removes this custom widget entirely).