Extract visitors from the grammar nodes and call makers in the peg generator (GH-28172)

Simplify the peg generator logic by extracting as much visitors as possible to disentangle the flow and separate concerns.

Tools/peg_generator/pegen/grammar_visualizer.py

@@ -1,7 +1,6 @@
 import argparse
 import sys
-
-from typing import Any, Iterator, Callable
+from typing import Any, Callable, Iterator
 
 from pegen.build import build_parser
 from pegen.grammar import Grammar, Rule