bpo-40941: Unify implicit and explicit state in the frame and generator objects into a single value. (GH-20803)

* Merge gen and frame state variables into one.

* Replace stack pointer with depth in PyFrameObject. Makes code easier to read and saves a word of memory.

Lib/test/test_yield_from.py

@@ -938,6 +938,9 @@ class TestPEP380Operation(unittest.TestCase):
                 res.append(g1.throw(MyErr))
         except StopIteration:
             pass
+        except:
+            self.assertEqual(res, [0, 1, 2, 3])
+            raise
         # Check with close
         class MyIt(object):
             def __iter__(self):