Visual Shader Editor: right click menu gets cropped

[noidexe]

Godot version:
3.1.beta.calinou.42ce497

OS/device including version:
Linux 64

Issue description:
On the visual shader editor dock, the right click menu might get cropped(see screenshot 1) or not fit on screen depending on screen resolution(see screenshot 2).
There are two causes for this:

• The mouse pointer always marks the top left position of the menu. This is different to how it works in most OSs.
• If the menu is taller than the screen it doesn't get split in two parts.

Screenshot 1:

Screenshot 2:

[Chaosus]

That menu should be ideally pinned to the left side of that graph(simular to visual script), current right-click behavior works ugly as hell