community: better support of pathlib paths in document loaders (#18396)

So this arose from the
https://github.com/langchain-ai/langchain/pull/18397 problem of document
loaders not supporting `pathlib.Path`.

This pull request provides more uniform support for Path as an argument.
The core ideas for this upgrade: 
- if there is a local file path used as an argument, it should be
supported as `pathlib.Path`
- if there are some external calls that may or may not support Pathlib,
the argument is immidiately converted to `str`
- if there `self.file_path` is used in a way that it allows for it to
stay pathlib without conversion, is is only converted for the metadata.

Twitter handle: https://twitter.com/mwmajewsk

libs/community/langchain_community/document_loaders/vsdx.py

@@ -1,7 +1,8 @@
 import os
 import tempfile
 from abc import ABC
-from typing import List
+from pathlib import Path
+from typing import List, Union
 from urllib.parse import urlparse
 
 import requests
@@ -13,9 +14,9 @@ from langchain_community.document_loaders.parsers import VsdxParser
 
 
 class VsdxLoader(BaseLoader, ABC):
-    def __init__(self, file_path: str):
+    def __init__(self, file_path: Union[str, Path]):
         """Initialize with file path."""
-        self.file_path = file_path
+        self.file_path = str(file_path)
         if "~" in self.file_path:
             self.file_path = os.path.expanduser(self.file_path)