[SymForce-External] Add update_template_data to CodegenConfig

Add update_template_data to CodegenConfig

This review adds one small method to `CodegenConfig`, with the intention of making it easier to support additional languages:

- `update_template_data`, which allows `CodegenConfig` subclasses to pass additional fields or functions to the templating engine.

Closes #186

GitOrigin-RevId: 222d3132e0a98723454bcd4390f2215457a0e7cb

symforce/codegen/codegen.py

@@ -538,8 +538,9 @@ def generate_function(
         self.namespace = namespace
 
         template_data = dict(self.common_data(), spec=self)
-        template_dir = self.config.template_dir()
+        self.config.update_template_data(data=template_data)
 
+        template_dir = self.config.template_dir()
         backend_name = self.config.backend_name()
         if skip_directory_nesting:
             out_function_dir = output_dir

symforce/codegen/codegen_config.py

@@ -136,3 +136,13 @@ def format_eigen_lcm_accessor(key: str, i: int) -> str:
         Format accessor for eigen_lcm types.
         """
         pass
+
+    def update_template_data(self, data: T.Dict[str, T.Any]) -> None:
+        """
+        Derived classes may override this to customize the "template data" dict. This dict
+        is passed to jinja at code-generation time.
+
+        Args:
+            data: Dict passed by Codegen. The function should modify this in-place.
+        """
+        pass