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
```

docs/docs/integrations/chat/google_generative_ai.ipynb

@@ -151,7 +151,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "from langchain.schema.messages import HumanMessage, SystemMessage\n",
+    "from langchain_core.messages import HumanMessage, SystemMessage\n",
     "\n",
     "model = ChatGoogleGenerativeAI(model=\"gemini-pro\", convert_system_message_to_human=True)\n",
     "model(\n",

docs/docs/integrations/llms/google_vertex_ai_palm.ipynb

@@ -415,7 +415,7 @@
    ],
    "source": [
     "from langchain.chat_models import ChatVertexAI\n",
-    "from langchain.schema.messages import HumanMessage\n",
+    "from langchain_core.messages import HumanMessage\n",
     "\n",
     "llm = ChatVertexAI(model_name=\"gemini-ultra-vision\")\n",
     "\n",

docs/docs/integrations/providers/cohere.mdx

@@ -49,7 +49,7 @@ print(llm.invoke("Come up with a pet name"))
 ```python
 from langchain.chat_models import ChatCohere
 from langchain.retrievers import CohereRagRetriever
-from langchain.schema.document import Document
+from langchain_core.documents import Document
 
 rag = CohereRagRetriever(llm=ChatCohere())
 print(rag.get_relevant_documents("What is cohere ai?"))
@@ -60,7 +60,7 @@ print(rag.get_relevant_documents("What is cohere ai?"))
 ```python
 from langchain.chat_models import ChatCohere
 from langchain.retrievers import CohereRagRetriever
-from langchain.schema.document import Document
+from langchain_core.documents import Document
 
 rag = CohereRagRetriever(llm=ChatCohere())
 print(rag.get_relevant_documents("What is cohere ai?"))

docs/docs/integrations/providers/vectara/vectara_summary.ipynb

@@ -76,9 +76,9 @@
    "source": [
     "from langchain.embeddings import FakeEmbeddings\n",
     "from langchain.prompts import ChatPromptTemplate\n",
-    "from langchain.schema.output_parser import StrOutputParser\n",
-    "from langchain.schema.runnable import RunnableLambda, RunnablePassthrough\n",
-    "from langchain.vectorstores import Vectara"
+    "from langchain.vectorstores import Vectara\n",
+    "from langchain_core.output_parsers import StrOutputParser\n",
+    "from langchain_core.runnables import RunnableLambda, RunnablePassthrough"
    ]
   },
   {

docs/docs/integrations/retrievers/fleet_context.ipynb

@@ -36,9 +36,9 @@
     "from langchain.embeddings import OpenAIEmbeddings\n",
     "from langchain.retrievers import MultiVectorRetriever\n",
     "from langchain.schema import Document\n",
-    "from langchain.schema.storage import BaseStore\n",
-    "from langchain.schema.vectorstore import VectorStore\n",
     "from langchain.vectorstores import FAISS\n",
+    "from langchain_core.stores import BaseStore\n",
+    "from langchain_core.vectorstores import VectorStore\n",
     "\n",
     "\n",
     "def load_fleet_retriever(\n",

docs/docs/integrations/vectorstores/jaguar.ipynb

@@ -58,10 +58,10 @@
     "from langchain.embeddings.openai import OpenAIEmbeddings\n",
     "from langchain.llms import OpenAI\n",
     "from langchain.prompts import ChatPromptTemplate\n",
-    "from langchain.schema.output_parser import StrOutputParser\n",
-    "from langchain.schema.runnable import RunnablePassthrough\n",
     "from langchain.text_splitter import CharacterTextSplitter\n",
     "from langchain_community.vectorstores.jaguar import Jaguar\n",
+    "from langchain_core.output_parsers import StrOutputParser\n",
+    "from langchain_core.runnables import RunnablePassthrough\n",
     "\n",
     "\"\"\" \n",
     "Load a text file into a set of documents \n",