community[major], core[patch], langchain[patch], experimental[patch]: Create langchain-community (#14463)

Moved the following modules to new package langchain-community in a backwards compatible fashion:

```
mv langchain/langchain/adapters community/langchain_community
mv langchain/langchain/callbacks community/langchain_community/callbacks
mv langchain/langchain/chat_loaders community/langchain_community
mv langchain/langchain/chat_models community/langchain_community
mv langchain/langchain/document_loaders community/langchain_community
mv langchain/langchain/docstore community/langchain_community
mv langchain/langchain/document_transformers community/langchain_community
mv langchain/langchain/embeddings community/langchain_community
mv langchain/langchain/graphs community/langchain_community
mv langchain/langchain/llms community/langchain_community
mv langchain/langchain/memory/chat_message_histories community/langchain_community
mv langchain/langchain/retrievers community/langchain_community
mv langchain/langchain/storage community/langchain_community
mv langchain/langchain/tools community/langchain_community
mv langchain/langchain/utilities community/langchain_community
mv langchain/langchain/vectorstores community/langchain_community
mv langchain/langchain/agents/agent_toolkits community/langchain_community
mv langchain/langchain/cache.py community/langchain_community
mv langchain/langchain/adapters community/langchain_community
mv langchain/langchain/callbacks community/langchain_community/callbacks
mv langchain/langchain/chat_loaders community/langchain_community
mv langchain/langchain/chat_models community/langchain_community
mv langchain/langchain/document_loaders community/langchain_community
mv langchain/langchain/docstore community/langchain_community
mv langchain/langchain/document_transformers community/langchain_community
mv langchain/langchain/embeddings community/langchain_community
mv langchain/langchain/graphs community/langchain_community
mv langchain/langchain/llms community/langchain_community
mv langchain/langchain/memory/chat_message_histories community/langchain_community
mv langchain/langchain/retrievers community/langchain_community
mv langchain/langchain/storage community/langchain_community
mv langchain/langchain/tools community/langchain_community
mv langchain/langchain/utilities community/langchain_community
mv langchain/langchain/vectorstores community/langchain_community
mv langchain/langchain/agents/agent_toolkits community/langchain_community
mv langchain/langchain/cache.py community/langchain_community
```

Moved the following to core
```
mv langchain/langchain/utils/json_schema.py core/langchain_core/utils
mv langchain/langchain/utils/html.py core/langchain_core/utils
mv langchain/langchain/utils/strings.py core/langchain_core/utils
cat langchain/langchain/utils/env.py >> core/langchain_core/utils/env.py
rm langchain/langchain/utils/env.py
```

See .scripts/community_split/script_integrations.sh for all changes

libs/community/tests/integration_tests/retrievers/test_arxiv.py

@@ -0,0 +1,50 @@
+"""Integration test for Arxiv API Wrapper."""
+from typing import List
+
+import pytest
+from langchain_core.documents import Document
+
+from langchain_community.retrievers import ArxivRetriever
+
+
+@pytest.fixture
+def retriever() -> ArxivRetriever:
+    return ArxivRetriever()
+
+
+def assert_docs(docs: List[Document], all_meta: bool = False) -> None:
+    for doc in docs:
+        assert doc.page_content
+        assert doc.metadata
+        main_meta = {"Published", "Title", "Authors", "Summary"}
+        assert set(doc.metadata).issuperset(main_meta)
+        if all_meta:
+            assert len(set(doc.metadata)) > len(main_meta)
+        else:
+            assert len(set(doc.metadata)) == len(main_meta)
+
+
+def test_load_success(retriever: ArxivRetriever) -> None:
+    docs = retriever.get_relevant_documents(query="1605.08386")
+    assert len(docs) == 1
+    assert_docs(docs, all_meta=False)
+
+
+def test_load_success_all_meta(retriever: ArxivRetriever) -> None:
+    retriever.load_all_available_meta = True
+    retriever.load_max_docs = 2
+    docs = retriever.get_relevant_documents(query="ChatGPT")
+    assert len(docs) > 1
+    assert_docs(docs, all_meta=True)
+
+
+def test_load_success_init_args() -> None:
+    retriever = ArxivRetriever(load_max_docs=1, load_all_available_meta=True)
+    docs = retriever.get_relevant_documents(query="ChatGPT")
+    assert len(docs) == 1
+    assert_docs(docs, all_meta=True)
+
+
+def test_load_no_result(retriever: ArxivRetriever) -> None:
+    docs = retriever.get_relevant_documents("1605.08386WWW")
+    assert not docs