Trigger popup menu with long press

For [ImageJ.JS](https://ij.imjoy.io) on touch screen devices, would be nice to emulate the right click by pressing longer (e.g 2s). For example, in the image window (or in the toolbar), trigger the popup menu when we do long pressing.

Start by locating the ImageJ.JS image-window and toolbar popup-menu entry points mentioned in the issue, then trace how right-click actions are handled on touch devices. The work is done when a long press, such as the suggested two seconds, opens the same popup menu in both areas.

Written by the indexing model from the issue text.