[dynamo] implement framelocals mapping as c++ object (#140063)

Implements https://github.com/pytorch/pytorch/issues/93753 - move frame local guard accessors to C++.

Before, we used dict accessors on a Python dict representing the frame's fastlocals that we manually build. We move this accessor to C++ and additionally use the fastlocal index whenever possible.

Some implementation notes:
- `FrameLocalsMapping` is now initialized as a C++ vector of `PyObject`s. We do not just use the frame's localsplus/fastlocals buffer because we also unbox cells.
- `FrameLocalsMapping` can still be converted into a Python dict representing the frame's fastlocals, but it is done lazily.
- We update `LeafGuard`, `GuardAccessor`, and `GuardManager`'s `check_nopybind` methods to accept `FrameLocalsMapping`. By default, we convert the `FrameLocalsMapping` to a Python dict and run the original `check_nopybind` on it, but in some cases, conversion is not needed.
- We add a new guard accessor `FrameLocalsGuardAccessor`, which is similar to `DictGetItemGuardAccessor` but has special handling for `FrameLocalsMapping`. We create a separate class to emphasize different use cases, but we could probably combine these two (can do in a follow up)

dynamo_guard_eval.py microbenchmark update:
- 713.2us -> 630.0us (3.10)
- 598.8us -> 530.7us (3.12)

Other followups:
- Add `FrameLocalsMapping` version for `check_verbose_nopybind` in order to match behavior between `check_nopybind` and `check_verbose_nopybind`. This can prevent difficult debugging situations where guards fail (`check_nopybind` returns false) but no guard error message is generated (`check_verbose_nopybind` succeeds).
- Rewrite the `SHAPE_ENV` guard into C++ - it is a fairly common guard that results in `FrameLocalsMapping` needing to convert to a dict

Pull Request resolved: https://github.com/pytorch/pytorch/pull/140063
Approved by: https://github.com/jansel
ghstack dependencies: #142117, #142430

torch/_dynamo/testing.py

@@ -207,7 +207,7 @@ def debug_insert_nops(
         torch_function_mode_stack=[],
     )
 
-    return GuardedCode(code, CheckFunctionManager(graph).guard_manager, CompileId(0, 0))  # type: ignore[arg-type]
+    return GuardedCode(code, CheckFunctionManager(frame.f_code, graph).guard_manager, CompileId(0, 0))  # type: ignore[arg-type]
 
 
 class CompileCounter: