Refactor print_function to use a new function called dump_function

[gussmith23]

On the Rust side, I would like to have access to the functions printed by print_function. @oflatt suggested a simple refactor, adding a dump_function function which dumps the Term objects, and then refactoring print_function to use dump_function. Then I can use dump_function to achieve my own goal.

Feel free to assign to me.

[gussmith23]

Turns out this is actually done! EGraph::function_to_dag.

Opened an issue to document the function: #367

[saulshanabrook]

Oh cool! There is an open issue in the Python bindings to expose print function, but I wasn't sure if I could get at the data. Nice to know that it's possible egraphs-good/egglog-python#124