[pyflakes] add backwards compatibility module (#11910)

stubs/pyflakes/pyflakes/scripts/pyflakes.pyi

@@ -0,0 +1,8 @@
+__all__ = ["check", "checkPath", "checkRecursive", "iterSourceCode", "main"]
+from pyflakes.api import (
+    check as check,
+    checkPath as checkPath,
+    checkRecursive as checkRecursive,
+    iterSourceCode as iterSourceCode,
+    main as main,
+)