patch: remove usage of llm, chat model __call__ (#20788)

- `llm(prompt)` -> `llm.invoke(prompt)`
- `llm(prompt=prompt` -> `llm.invoke(prompt)` (same with `messages=`)
- `llm(prompt, callbacks=callbacks)` -> `llm.invoke(prompt,
config={"callbacks": callbacks})`
- `llm(prompt, **kwargs)` -> `llm.invoke(prompt, **kwargs)`

libs/community/langchain_community/llms/openllm.py

@@ -63,7 +63,7 @@ class OpenLLM(LLM):
                 model_name='flan-t5',
                 model_id='google/flan-t5-large',
             )
-            llm("What is the difference between a duck and a goose?")
+            llm.invoke("What is the difference between a duck and a goose?")
 
     For all available supported models, you can run 'openllm models'.