Support custom template number types to be GDB pretty-printed

The requested changes solve the following issue. Consider the following number type autodiff::Real<4, double> (e.g., a 4th order number type with automatic differentiation capabilities. Because of how template_params are constructed in printer.py, using the m.split(',') logic, we get a list of strings as follows when using this type in an Eigen vector:

["autodiff::Real<4", "double>", "-1", "1", "0", "-1", "1"]

The code changes in this merge request solve this issue. It produces a template_params list as follows:

["autodiff::Real<4, double>", "-1", "1", "0", "-1", "1"]