bpo-45947: Place dict and values pointer at fixed (negative) offset just before GC header. (GH-29879)
* Place __dict__ immediately before GC header for plain Python objects.
* Fix up lazy dict creation logic to use managed dict pointers.
* Manage values pointer, placing them directly before managed dict pointers.
* Convert hint-based load/store attr specialization target managed dict classes.
* Specialize LOAD_METHOD for managed dict objects.
* Remove unsafe _PyObject_GC_Calloc function.
* Remove unsafe _PyObject_GC_Malloc() function.
* Add comment explaning use of Py_TPFLAGS_MANAGED_DICT.
19 files changed
