feat(api): Implement variable mapping extraction for `IfElseNode`

This allows us to extract referenced variables from `IfElseNode` configurations.

api/core/workflow/nodes/if_else/if_else_node.py

@@ -1,4 +1,5 @@
-from typing import Literal
+from collections.abc import Mapping, Sequence
+from typing import Any, Literal
 
 from typing_extensions import deprecated
 
@@ -91,6 +92,22 @@ class IfElseNode(BaseNode[IfElseNodeData]):
 
         return data
 
+    @classmethod
+    def _extract_variable_selector_to_variable_mapping(
+        cls,
+        *,
+        graph_config: Mapping[str, Any],
+        node_id: str,
+        node_data: IfElseNodeData,
+    ) -> Mapping[str, Sequence[str]]:
+        var_mapping: dict[str, list[str]] = {}
+        for case in node_data.cases or []:
+            for condition in case.conditions:
+                key = "{}.#{}#".format(node_id, ".".join(condition.variable_selector))
+                var_mapping[key] = condition.variable_selector
+
+        return var_mapping
+
 
 @deprecated("This function is deprecated. You should use the new cases structure.")
 def _should_not_use_old_function(