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/unit_tests/document_loaders/test_readthedoc.py

@@ -0,0 +1,54 @@
+from pathlib import Path
+
+import pytest
+
+from langchain_community.document_loaders.readthedocs import ReadTheDocsLoader
+
+PARENT_DIR = Path(__file__).parent / "test_docs" / "readthedocs"
+
+
+@pytest.mark.requires("bs4")
+def test_main_id_main_content() -> None:
+    loader = ReadTheDocsLoader(PARENT_DIR / "main_id_main_content")
+    documents = loader.load()
+    assert len(documents[0].page_content) != 0
+
+
+@pytest.mark.requires("bs4")
+def test_div_role_main() -> None:
+    loader = ReadTheDocsLoader(PARENT_DIR / "div_role_main")
+    documents = loader.load()
+    assert len(documents[0].page_content) != 0
+
+
+@pytest.mark.requires("bs4")
+def test_custom() -> None:
+    loader = ReadTheDocsLoader(
+        PARENT_DIR / "custom",
+        custom_html_tag=("article", {"role": "main"}),
+    )
+    documents = loader.load()
+    assert len(documents[0].page_content) != 0
+
+
+@pytest.mark.requires("bs4")
+def test_nested_html_structure() -> None:
+    loader = ReadTheDocsLoader(PARENT_DIR / "nested_html_structure")
+    documents = loader.load()
+    assert documents[0].page_content == "Hello World!"
+
+
+@pytest.mark.requires("bs4")
+def test_index_page() -> None:
+    loader = ReadTheDocsLoader(PARENT_DIR / "index_page", exclude_links_ratio=0.5)
+    documents = loader.load()
+    assert len(documents[0].page_content) == 0
+
+
+@pytest.mark.requires("bs4")
+def test_empty() -> None:
+    loader = ReadTheDocsLoader(
+        PARENT_DIR / "custom",
+    )
+    documents = loader.load()
+    assert len(documents[0].page_content) == 0