langchain[patch]: deprecate various chains (#25310)

- [x] NatbotChain: move to community, deprecate langchain version.
Update to use `prompt | llm | output_parser` instead of LLMChain.
- [x] LLMMathChain: deprecate + add langgraph replacement example to API
ref
- [x] HypotheticalDocumentEmbedder (retriever): update to use `prompt |
llm | output_parser` instead of LLMChain
- [x] FlareChain: update to use `prompt | llm | output_parser` instead
of LLMChain
- [x] ConstitutionalChain: deprecate + add langgraph replacement example
to API ref
- [x] LLMChainExtractor (document compressor): update to use `prompt |
llm | output_parser` instead of LLMChain
- [x] LLMChainFilter (document compressor): update to use `prompt | llm
| output_parser` instead of LLMChain
- [x] RePhraseQueryRetriever (retriever): update to use `prompt | llm |
output_parser` instead of LLMChain

libs/community/langchain_community/chains/natbot/__init__.py

@@ -0,0 +1,8 @@
+"""Implement a GPT-3 driven browser.
+
+Heavily influenced from https://github.com/nat/natbot
+"""
+
+from langchain_community.chains.natbot.base import NatBotChain
+
+__all__ = ["NatBotChain"]

libs/community/langchain_community/chains/natbot/base.py

@@ -0,0 +1,3 @@
+from langchain.chains import NatBotChain
+
+__all__ = ["NatBotChain"]

libs/community/langchain_community/chains/natbot/crawler.py

@@ -0,0 +1,7 @@
+from langchain.chains.natbot.crawler import (
+    Crawler,
+    ElementInViewPort,
+    black_listed_elements,
+)
+
+__all__ = ["ElementInViewPort", "Crawler", "black_listed_elements"]

libs/community/langchain_community/chains/natbot/prompt.py

@@ -0,0 +1,3 @@
+from langchain.chains.natbot.prompt import PROMPT
+
+__all__ = ["PROMPT"]