C extensions can't swap out live frames in CPython 3.11

[brandtbucher]

CPython 3.11 makes several major changes to how frame objects are used and represented internally:

• bpo-44032: Move data stack to thread from FrameObject. python/cpython#26076
• bpo-44590: Lazily allocate frame objects python/cpython#27077
• bpo-45637: Store the frame pointer in the cframe python/cpython#29267

I've opened a CPython issue to discuss the impact of these changes on Greenlet, and what can be done to help fix the affected code.