Provide support for IJ2 menu separators

[karlduderstadt]

The new IJ2 method for specifying command placement within menus can support the creation of separators or dividing lines between menu items. Unfortunately, this feature is not implemented in the IJ1MenuWrapper inner class in the IJ1Helper class responsible for adding IJ2 commands in legacy mode.

If the menu weight parameter is greater than one between two consecutive commands in a menu, a separator will be added in between. This feature is currently implemented in scijava-common and fully realized in scijava-ui-swing when using Modern Mode. It would be wonderful if this feature was also available in legacy mode.

[imagesc-bot]

This issue has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/specify-plugin-order-in-submenus-in-ij2/19321/10