Some IonPyDict Methods Behave Like Python 2 Dict

[cheqianh]

Description:

Specifically, item() and iteritems(). The original conversation is available in https://github.com/amazon-ion/ion-python/pull/284#discussion_r1319185416.

In details, in Python 2:

dict.items()

Description: Return a **list** of the dictionary's (key, value) tuple pairs.

in Python3:

dict.items()

Description: Return a **view** object of the dictionary's (key, value) pairs.

We are still returnning a whole list, and we still have iteritems() which python 3 has removed it.