Add the ability to run third-party stubtest on Windows or MacOS when needed (#8923)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

tests/get_packages.py

@@ -0,0 +1,23 @@
+#!/usr/bin/env python3
+import os
+import sys
+
+import tomli
+
+platform = sys.platform
+distributions = sys.argv[1:]
+if not distributions:
+    distributions = os.listdir("stubs")
+
+metadata_mapping = {
+    "linux": "apt_dependencies",
+    # We could add others here if we run into stubs that need it:
+    # "darwin": "brew_dependencies",
+    # "win32": "choco_dependencies",
+}
+
+if platform in metadata_mapping:
+    for distribution in distributions:
+        with open(f"stubs/{distribution}/METADATA.toml", "rb") as file:
+            for package in tomli.load(file).get("tool", {}).get("stubtest", {}).get(metadata_mapping[platform], []):
+                print(package)