Multiple context menus

[jpnurmi]

Occasionally, two context menus open on top of each other at the same time.

[jpnurmi]

When you right-click anywhere in the background, it's supposed to show a context menu without instance-specific items.

When you right-click a specific instance row, it's supposed to show a context menu with the respective instance-specific items.

[jpnurmi]

There are two overlapping gesture detectors. Sometimes, both menus are shown at the same time because the gesture detector on top leaks clicks through to the gesture detector below. I've reported this as a Flutter bug:

• https://github.com/flutter/flutter/issues/116650