Fix type hints for enums referring to ttypes

[earangol-stripe]

Summary

Changes type hints for enum values to ints instead of the class type.

Why / Goal

Current type hints for enum values are incorrect because of the way Thrift compiles them in Python. E.g. for ttypes.Accuracy:

class Accuracy(object):
    TEMPORAL = 0
    SNAPSHOT = 1

So a parameter defined as def my_func(accuracy: ttypes.Accuracy = ttypes.Accuracy.TEMPORAL) ends up being an incorrect assignment because TEMPORAL is just an int.

To improve usability with IDEs and lint tools, along the same lines as #969.

Test Plan

• Added Unit Tests
• Covered by existing CI
• Integration tested

Checklist

• Documentation update

Reviewers

[earangol-stripe]

I just realized there is an option in the Thrift compiler to generate Python enums: py:enum. That looks better to me, though it might not be a safe change. I'll put this PR on hold and play with that option instead.