Ensure that label names in processor start with capital letter

The change is needed since even if ANTLR enables to have lower-case
label names, but it will convert them to start with capital letter
eventually, since the Context class created from them must be capital.
Since the name of this Context class will be used by grammarinator-parse
to create nodes from labelled rules, we need to ensure a common
naming schema.

grammarinator/tool/processor.py

@@ -906,6 +906,9 @@ def build_expr(node, parent_id):
  nonlocal alt_idx
  conditions = [find_conditions(child) for child in children]
  labels = [str(child.identifier().TOKEN_REF() or child.identifier().RULE_REF()) for child in children if child.identifier()] if isinstance(node, ANTLRv4Parser.RuleAltListContext) else []
+ # Ensure to start labels with capital letter, since ANTLR will also create a context with capital start character.
+ # It's important to keep them in sync since grammarinator-parse will use this graph for comparison.
+ labels = [label[0].upper() + label[1:] for label in labels]
  recurring_labels = {name for name, cnt in Counter(labels).items() if cnt > 1}
  assert len(labels) == 0 or len(labels) == len(children)
  alt_id = graph.add_node(AlternationNode(idx=alt_idx, conditions=append_unique(graph.alt_conds, conditions) if all(isfloat(cond) for cond in conditions) else conditions, rule_id=rule.id))