langchain[patch], experimental[patch]: replace langchain.schema imports (#15410)

Import from core instead.

Ran:
```bash
git grep -l 'from langchain.schema\.output_parser' | xargs -L 1 sed -i '' "s/from\ langchain\.schema\.output_parser/from\ langchain_core.output_parsers/g"
git grep -l 'from langchain.schema\.messages' | xargs -L 1 sed -i '' "s/from\ langchain\.schema\.messages/from\ langchain_core.messages/g"
git grep -l 'from langchain.schema\.document' | xargs -L 1 sed -i '' "s/from\ langchain\.schema\.document/from\ langchain_core.documents/g"
git grep -l 'from langchain.schema\.runnable' | xargs -L 1 sed -i '' "s/from\ langchain\.schema\.runnable/from\ langchain_core.runnables/g"
git grep -l 'from langchain.schema\.vectorstore' | xargs -L 1 sed -i '' "s/from\ langchain\.schema\.vectorstore/from\ langchain_core.vectorstores/g"
git grep -l 'from langchain.schema\.language_model' | xargs -L 1 sed -i '' "s/from\ langchain\.schema\.language_model/from\ langchain_core.language_models/g"
git grep -l 'from langchain.schema\.embeddings' | xargs -L 1 sed -i '' "s/from\ langchain\.schema\.embeddings/from\ langchain_core.embeddings/g"
git grep -l 'from langchain.schema\.storage' | xargs -L 1 sed -i '' "s/from\ langchain\.schema\.storage/from\ langchain_core.stores/g"
git checkout master libs/langchain/tests/unit_tests/schema/
make format
cd libs/experimental
make format
cd ../langchain
make format
```

templates/sql-research-assistant/sql_research_assistant/chain.py

@@ -1,5 +1,5 @@
 from langchain.pydantic_v1 import BaseModel
-from langchain.schema.runnable import RunnablePassthrough
+from langchain_core.runnables import RunnablePassthrough
 
 from sql_research_assistant.search.web import chain as search_chain
 from sql_research_assistant.writer import chain as writer_chain

templates/sql-research-assistant/sql_research_assistant/search/sql.py

@@ -4,9 +4,9 @@ from langchain.chat_models import ChatOllama, ChatOpenAI
 from langchain.memory import ConversationBufferMemory
 from langchain.prompts import ChatPromptTemplate
 from langchain.pydantic_v1 import BaseModel
-from langchain.schema.output_parser import StrOutputParser
-from langchain.schema.runnable import RunnablePassthrough
 from langchain.utilities import SQLDatabase
+from langchain_core.output_parsers import StrOutputParser
+from langchain_core.runnables import RunnablePassthrough
 
 # Add the LLM downloaded from Ollama
 ollama_llm = "llama2"

templates/sql-research-assistant/sql_research_assistant/search/web.py

@@ -5,15 +5,15 @@ import requests
 from bs4 import BeautifulSoup
 from langchain.chat_models import ChatOpenAI
 from langchain.prompts import ChatPromptTemplate
-from langchain.schema.messages import SystemMessage
-from langchain.schema.output_parser import StrOutputParser
-from langchain.schema.runnable import (
+from langchain.utilities import DuckDuckGoSearchAPIWrapper
+from langchain_core.messages import SystemMessage
+from langchain_core.output_parsers import StrOutputParser
+from langchain_core.runnables import (
     Runnable,
     RunnableLambda,
     RunnableParallel,
     RunnablePassthrough,
 )
-from langchain.utilities import DuckDuckGoSearchAPIWrapper
 
 from sql_research_assistant.search.sql import sql_answer_chain
 

templates/sql-research-assistant/sql_research_assistant/writer.py

@@ -1,7 +1,7 @@
 from langchain.chat_models import ChatOpenAI
 from langchain.prompts import ChatPromptTemplate
-from langchain.schema.output_parser import StrOutputParser
-from langchain.schema.runnable import ConfigurableField
+from langchain_core.output_parsers import StrOutputParser
+from langchain_core.runnables import ConfigurableField
 
 WRITER_SYSTEM_PROMPT = "You are an AI critical thinker research assistant. Your sole purpose is to write well written, critically acclaimed, objective and structured reports on given text."  # noqa: E501