nkIdentDefs is annoying to work with #25303
Description
Early in the frontend we should remove nkIdentDefs as it serves no purpose. Instead the tuple of 5 entries (var/let/const symbol exportMarker/empty pragmas typ value) should be used. This would also simplify the compiler anywere we have to deal with nkPostfix nodes (which serve no purpose but to annotate an identifier with an export marker).