Implemented by extending `collections.abc.MutableSet` and backing it with a dictionary, which is ordered. From collections.abc.MutableSet:
```
A mutable set is a finite, iterable container.
This class provides concrete generic implementations of all
methods except for __contains__, __iter__, __len__,
add(), and discard().
```
In addition to implementing those methods I also had to define some methods of python's set which were not implemented in MutableSet.
I reused the test from my python's lib. There were a few instances of tests that didnt pass because edge case behavior that is not necessary to reimplement
- support self-referencing repr
- erroring when an member's `__eq__` function would modify the set itself
- MutableSet supports Iterables as inputs, but not sequences (pretty rare..)
- Some specifics of exact equivalent type errors being thrown
- [The protocol for automatic conversion to immutable](https://docs.python.org/2/library/sets.html#protocol-for-automatic-conversion-to-immutable)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/130003
Approved by: https://github.com/aorenste
