Pasting variable nodes from one graph to another is problematic

[trobins78]

The variables are successfully pasted, but they are not recognized by the recipient graph. In other words, they aren't added as variables to the graph that is pasted to. In some cases, manually recreating the variables seems to work fine, but I've also encountered errors that I couldn't rectify, even by deleting all variables and recreating them.

To Reproduce

Steps to reproduce the behavior:

1. Paste variable nodes from one graph to another

Expected behavior

1. It would be nice if it the 'copied' variables were added as new variables in the recipient graph.
2. If there is a naming conflict (already a variable of same name), perhaps the newly added variable could have a suffix that made it obvious, so the user would easily see that it should be addressed. (i.e. conflicting name "Float1" becomes "Float1_DUPLICATE")
3. In order to make this feature complete, the original default values of the copied variables would be maintained.