Add specialization "families" for PEP 659 adaptive interpreter for LOAD_METHOD.

Background:

LOAD_METHOD is a compiler-level specialization of LOAD_ATTR. It's emitted with CALL_METHOD for calls of the form o.meth(), where o is not a top-level import. When this was added in 3.7, it brought 20% faster method calls by avoiding creating a bound method object.

Specialization

The specialization families for LOAD_METHOD are very similar to LOAD_ATTR (#52) and we can reuse many ideas and code. The speedup comes from avoiding a _PyObject_GetMethod which does two things:

1. _PyType_Lookup (walk the MRO)
2. Check if meth is in o.__dict__ to make sure it's not an attribute.

There are one or two specializations which I'm optimistic for:

• LOAD_METHOD_WITH_HINT (see LOAD_ATTR_WITH_HINT) renamed to LOAD_METHOD_CACHED -- cache the descriptor object
• Optional: LOAD_METHOD_WITH_HINT_NO_DICT -- specialized form of LOAD_METHOD_WITH_HINT for objects with no __dict__

These specializations make sense, but will likely bring little speedup in macrobenchmarks, so we need more profiling:

• LOAD_METHOD_MODULE -- o is a module, almost same as specializing LOAD_ATTR_MODULE
• LOAD_METHOD_CLASS -- o is a class and meth is a classmethod

Also, I don't expect much speedups for builtin methods (e.g {1,2,3}.keys()). Their _PyType_Lookup should be cheap due to the existing type method cache. Classes with a long MRO will probably benefit the most.

Workbranch: python/cpython#27722