Change "rename this type variable" (etc.) text

[dhess]

Currently, we cannot select the nodes that provide binding names, only their binders. See hackworthltd/primer#1183.

Eventually, we'd like to be able to select these nodes, but until that happens, the only way to rename these bindings is to select their binders. Therefore, we should change the action labels that read "rename this type variable" (etc.) to "rename the binding" or something similar.