Python: Add copy of extractor tests

These get to live next to the existing library and query tests, and are
run as part of both the Python 2 and Python 3 language tests.

python/ql/test/extractor-tests/async/test.py

@@ -0,0 +1,27 @@
+
+def normal():
+    pass
+
+async def is_async():
+    pass
+
+def decorator(func):
+    return func
+
+@decorator
+def deco():
+    pass
+
+@decorator
+async def deco_async():
+    pass
+
+
+
+async def foo():
+    async for x in y:
+        async with a as b:
+            pass
+    await z
+
+