Added missing type information for encodings module (#5106)

Co-authored-by: Eric Traut <erictr@microsoft.com>

stdlib/encodings/__init__.pyi

@@ -1,7 +1,7 @@
-import codecs
-from typing import Any
+from codecs import CodecInfo
+from typing import Optional, Union
 
-def search_function(encoding: str) -> codecs.CodecInfo: ...
+class CodecRegistryError(LookupError, SystemError): ...
 
-# Explicitly mark this package as incomplete.
-def __getattr__(name: str) -> Any: ...
+def normalize_encoding(encoding: Union[str, bytes]) -> str: ...
+def search_function(encoding: str) -> Optional[CodecInfo]: ...