[encoding] Add win32_code_page_search_function (#14510)

Docs: https://docs.python.org/dev/library/codecs.html#encodings.win32_code_page_search_function

stdlib/encodings/__init__.pyi

@@ -1,3 +1,4 @@
+import sys
 from codecs import CodecInfo
 
 class CodecRegistryError(LookupError, SystemError): ...
@@ -5,5 +6,8 @@ class CodecRegistryError(LookupError, SystemError): ...
 def normalize_encoding(encoding: str | bytes) -> str: ...
 def search_function(encoding: str) -> CodecInfo | None: ...
 
+if sys.version_info >= (3, 14) and sys.platform == "win32":
+    def win32_code_page_search_function(encoding: str) -> CodecInfo | None: ...
+
 # Needed for submodules
 def __getattr__(name: str): ...  # incomplete module