qdrant: init package (#21146)

## Description

This PR introduces the new `langchain-qdrant` partner package, intending
to deprecate the community package.

## Changes

- Moved the Qdrant vector store implementation `/libs/partners/qdrant`
with integration tests.
- The conditional imports of the client library are now regular with
minor implementation improvements.
- Added a deprecation warning to
`langchain_community.vectorstores.qdrant.Qdrant`.
- Replaced references/imports from `langchain_community` with either
`langchain_core` or by moving the definitions to the `langchain_qdrant`
package itself.
- Updated the Qdrant vector store documentation to reflect the changes.

## Testing
- `QDRANT_URL` and
[`QDRANT_API_KEY`](583e36bf6b)
env values need to be set to [run integration
tests](d608c93d1f)
in the [cloud](https://cloud.qdrant.tech).
- If a Qdrant instance is running at `http://localhost:6333`, the
integration tests will use it too.
- By default, tests use an
[`in-memory`](https://github.com/qdrant/qdrant-client?tab=readme-ov-file#local-mode)
instance(Not comprehensive).

---------

Co-authored-by: Erick Friis <erick@langchain.dev>
Co-authored-by: Erick Friis <erickfriis@gmail.com>

libs/community/langchain_community/vectorstores/qdrant.py

@@ -22,6 +22,7 @@ from typing import (
 )
 
 import numpy as np
+from langchain_core._api.deprecation import deprecated
 from langchain_core.embeddings import Embeddings
 from langchain_core.runnables.config import run_in_executor
 from langchain_core.vectorstores import VectorStore
@@ -65,6 +66,9 @@ def sync_call_fallback(method: Callable) -> Callable:
     return wrapper
 
 
+@deprecated(
+    since="0.0.37", removal="0.3.0", alternative_import="langchain_qdrant.Qdrant"
+)
 class Qdrant(VectorStore):
     """`Qdrant` vector store.