Move common utility functions to a common library (#12773)

pyrightconfig.scripts_and_tests.json

@@ -2,9 +2,13 @@
     "$schema": "https://raw.githubusercontent.com/microsoft/pyright/main/packages/vscode-pyright/schemas/pyrightconfig.schema.json",
     "typeshedPath": ".",
     "include": [
+        "lib",
         "scripts",
         "tests",
     ],
+    "extraPaths": [
+        "lib",
+    ],
     "typeCheckingMode": "strict",
     // More of a lint. Unwanted for typeshed's own code.
     "reportImplicitStringConcatenation": "none",