Implement canonicalize() method in ASTNode

[mephenor]

in our research group we recently switched from using the libsbml
library to the jsbml library for our program due to performance issues.
In our old version we had an AST Node parser, that took a AST Node tree
and converted it into our internal node format. Therefore we used the
libsbml function "canonicalize()" that checked wether an AST Node of the
type "Name" is already a predefined function and if so it returned this
new AST Node. Jsbml is missing such a function.
So my question is, if the library does this implicitly and doesn't
return name nodes that could be other nodes or if there are any other
ways to achieve the same result as with the libsbml version.

Reported by: *anonymous