Implement deepClone and line/col number assignment for MethodNodes

As per the discussion on the grails mailing list to inject MethodNodes in GCL it would be handy if we could get groovy to do the work for us to create said MethodNode:

"let us define a text containing all methods we need. Then give that a
CompileUnit add a custom Operation for the convert step, where you
extract the methods. Then run the convert step and you are ready. I
could add a deepClone method, so that you can always have your own
method node... they are modified during the later steps. Only thing left
is to set the line/col information for these nodes. I could prepare that
if you want. Besides the changes for the cloning, it would be only a
small piece of code. An alternative is to extract that information each
time you create a class in grails... I don't think that is really an
option "