Issue #24619: New approach for tokenizing async/await.

This commit fixes how one-line async-defs and defs are tracked
by tokenizer.  It allows to correctly parse invalid code such
as:

>>> async def f():
...     def g(): pass
...     async = 10

and valid code such as:

>>> async def f():
...     async def g(): pass
...     await z

As a consequence, is is now possible to have one-line
'async def foo(): await ..' functions:

>>> async def foo(): return await bar()

1 files changed, 1 insertions, 1 deletions

diff --git a/Lib/test/badsyntax_async4.py b/Lib/test/badsyntax_async4.py
index 4afda40..d033b28 100644
--- a/Lib/test/badsyntax_async4.py
+++ b/Lib/test/badsyntax_async4.py
@@ -1,2 +1,2 @@
 async def foo():
-    async def foo(): await something()
+    await