Guard invalid python annotations for 3.8 / 3.9 (#848)

Summary:
Pull Request resolved: #848

This is blocking an open source release.

Note: there's a test failure still in OSS in one of these tests.
We do need to fix that, but unlike using illegal-for-python-3.9
syntax it doesn't make Pyre unreleasable.

Reviewed By: connernilsen

Differential Revision: D57218457

fbshipit-source-id: 4691f2ef8be0f88effb9ce0a490d82e8fda2fa35

tools/upgrade/commands/configurationless.py

@@ -5,6 +5,8 @@
 
 # pyre-strict
 
+from __future__ import annotations
+
 import argparse
 import json
 import logging

tools/upgrade/commands/strict_default.py

@@ -9,6 +9,7 @@
 strict_default contains a library for running a codemod across a codebase that turns pyre-strict on. Optionally, we can also remove the #pyre-strict and add #pyre-unsafe headers from files where the error count is below a certain threshhold.
 """
 
+from __future__ import annotations
 
 import argparse
 import logging

tools/upgrade/configuration.py

@@ -9,6 +9,7 @@
 TODO(T132414938) Add a module-level docstring
 """
 
+from __future__ import annotations
 
 import glob
 import json