Add a method to access the GridMap editor's current selection

[mav006]

Describe the project you are working on

I'm working on a 3D game. I want to use gridmaps for a couple of things. To make the gridmap more easy to use I'm adding the functionality of splitting gridmaps. I want to be able to select a part of grdmapA (with the shift + click selection that is implemented), hit a button, and then the selected part of the gridmapA separates from it and becomes gridmapB in my hierarchy.

Describe the problem or limitation you are having in your project

There is no way (that I have found) to access the cells I select with the shift + click selection box. Since I want to manipulate the selected cells specifically, I need to know which ones they are. I can see the whole selection process in the source code, but It would be great to have a simple function to access the selected cells.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Being able to manipulate only the parts of a gridmap the user wants through code can be useful. I already have another function I want to impolement that requires me to access the selection

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

One of the methods of the gridmap is
Array get_selected_cells()
It returns null if there is no selection, and returns an array of cell items

If this enhancement will not be used often, can it be worked around with a few lines of script?

The way to work aroudn this is to create your own selection method, which is what I'm going to use. But it is a very simple line since the code is done, I just need access to it.

Is there a reason why this should be core and not an add-on in the asset library?

It would allow people to make the addons