Convert Python type hinting to be PEP-585 Compliant (#4083)

Python [PEP-585](https://peps.python.org/pep-0585/) replaces a number of
`typing` module types with built-in equivalents and `collections.abc`
versions as of Python 3.9, with the aim of eventually removing the
`typing` module versions of these classes altogether. Since the minimum
required version of Python listed in the [Contribution Tools
document](https://github.com/carbon-language/carbon-lang/blob/trunk/docs/project/contribution_tools.md#main-tools)
is 3.9, the type hints in the various python files in the repo can be
updated to this style of type hint without a need for backwards
compatibility.

Feel free to close if this isn't a desired change at this time!

---------

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>

scripts/scripts_utils.py

@@ -14,7 +14,7 @@ from pathlib import Path
 import platform
 import shutil
 import time
-from typing import Dict, Optional
+from typing import Optional
 import urllib.request
 
 _BAZEL_TOOLS_URL = (
@@ -161,7 +161,7 @@ def _get_platform_ext() -> str:
         return ""
 
 
-def _select_hash(hashes: Dict[str, str], version: str) -> str:
+def _select_hash(hashes: dict[str, str], version: str) -> str:
     # Ensure the platform version is supported and has a hash.
     if version not in hashes:
         # If this because a platform support issue, we may need to print errors.