Issue #7537: CPython set/frozenset compatible FiniteSet interface

Is this something which we can have? My use case right now is simple: third party libraries which are written with CPython's standard set interface in mind, will continue to work.  My current use case is using ``matplotlib-venn`` (https://github.com/konstantint/matplotlib-venn). Here is how I would use it:

```
from sympy.sets.sets_compat import FiniteSet
import matplotlib.pyplot as plt
from matplotlib_venn import venn2

s1 = FiniteSet(1, 2, 3)
s2 = FiniteSet(2, 4, 6)

venn2(subsets= (s1, s2))
plt.show()
```