Add Copy-Paste functionality for Nodes

[ch0m5]

Problem

There's sometimes situations where it is faster, specially for duplicating structures, to copy and paste your current selection of Nodes that it is to recreate that structure from scratch. The 1st option is currently not possible.

Proposed Solution

In a similar fashion to moving several selected Nodes at once, we could include Copy/Cut/Paste functionalities to Nodes, so that Nodes can be selected and then easily duplicated or repositioned through these shortcuts. The existing Dictionary-based Save&Load system that exists for Nodes could be useful for this purpose.

Ideally, this feature should be included in the Undo/Redo system, so that using these actions can be undone and redone as you would for any other changes in the DialogueData file.

Additionally, as a user, I would expect for selected Nodes I've duplicated or moved to retain the connections between them, as in connections between the Nodes I've edited. I would not expect (nor desire) for Nodes that I've Cut+Paste or Duplicated to retain connections to Nodes I've not performed the same operation on, i.e. Nodes that I've "left out".

[nagidev]

Currently, the editor supports duplicating the selected nodes using CTRL+D, but I can see cases where copy/paste would be more useful, like copying nodes from one file to another. The idea of converting the selection into a temporary DialogueData resource and using it to copy/paste/duplicate is something I experimented in the past but it turned out to be a bit complicated for me. I'll definitely take a look into it again soon. Cheers!

[ch0m5]

I don't see this as a priority, but I feel it is a set of actions that feel really natural to execute, and when using the addon for the first time you expect it to be there. This holds little importance, but if we can add it eventually it would be a net positive for the addon imo.