Function from_scalar_fn_to_df_fn_impl 

pub(crate) async fn from_scalar_fn_to_df_fn_impl(
    f: &ScalarFunction,
    input_schema: &RelationDesc,
    extensions: &FunctionExtensions,
) -> Result<Arc<dyn PhysicalExpr>, Error>

Convert ScalarFunction to corresponding Datafusion’s [PhysicalExpr]