[3.9] bpo-41194: The _ast module cannot be loaded more than once (GH-21290) (GH-21292)

* bpo-41194: Pass module state in Python-ast.c (GH-21284)

Rework asdl_c.py to pass the module state to functions in
Python-ast.c, instead of using astmodulestate_global.

Handle also PyState_AddModule() failure in init_types().

(cherry picked from commit 74419f0)

* bpo-41194: The _ast module cannot be loaded more than once (GH-21290)

Fix a crash in the _ast module: it can no longer be loaded more than
once. It now uses a global state rather than a module state.

* Move _ast module state: use a global state instead.
* Set _astmodule.m_size to -1, so the extension cannot be loaded more
  than once.

(cherry picked from commit 91e1bc1)

Author: vstinner

Misc/NEWS.d/next/Library/2020-07-03-13-15-08.bpo-41194.djrKjs.rst

@@ -0,0 +1,2 @@
+Fix a crash in the ``_ast`` module: it can no longer be loaded more than once.
+It now uses a global state rather than a module state.