Unify the handling of infinite quantification limit across tree codecs

From now, not only the flatbuffers but also the json tree codec represents
the infinite quantification limit with the value of -1.

grammarinator/tool/tree_codec.py

@@ -137,7 +137,7 @@ def _rule_to_dict(node):
             if isinstance(node, UnparserRuleQuantified):
                 return {'t': 'qd', 'c': node.children}
             if isinstance(node, UnparserRuleQuantifier):
-                return {'t': 'q', 'i': node.idx, 'b': node.start, 'e': node.stop, 'c': node.children}
+                return {'t': 'q', 'i': node.idx, 'b': node.start, 'e': node.stop if node.stop != inf else -1, 'c': node.children}
             raise AssertionError
         return json.dumps(root, default=_rule_to_dict).encode(encoding=self._encoding, errors=self._encoding_errors)
 
@@ -152,7 +152,7 @@ def _dict_to_rule(dct):
             if dct['t'] == 'qd':
                 return UnparserRuleQuantified(children=dct['c'])
             if dct['t'] == 'q':
-                return UnparserRuleQuantifier(idx=dct['i'], start=dct['b'], stop=dct['e'], children=dct['c'])
+                return UnparserRuleQuantifier(idx=dct['i'], start=dct['b'], stop=dct['e'] if dct['e'] != -1 else inf, children=dct['c'])
             raise json.JSONDecodeError
 
         try: