We need to raise AttributeError for non-existing dunder methods like
'__deepcopy__' or '__getstate__', because deepcopy() and pickle.load()
test for these on the instance using getattr() and treat the resulting
AttributeError as a signal that the object doesn't implement these custom
hooks. If we don't do that, we enter an infinite recursion as we attempt
to look up the missing dunder methods in the 'rawDict' dictionary,
because 'rawDict' is set inside __init__, but __init__ is not invoked
while unpickling (only __new__ is); thus self.rawDict is also missing
and __getattr__ is invoked with argument 'rawDict' again and again until
it crashes with RecursionError. Phew.
Fixes https://github.com/fonttools/fonttools/pull/1488
649dc49dba