PR: Add utility functions that convert between ints and Qt Enums (compat.py)

[zjp]

This PR implements the functions I asked about in #356

[zjp]

I can see some failures on PySide2 that I'll address when I get to a machine that has a binary PySide2 available (I usually work on an arm64 mac).

[coveralls]

coverage: 90.164% (+0.1%) from 90.016% when pulling 72e9f449b282ed039e44d30f19a5828d18c9b642 on zjp:int_as_enum into 0f7b181e45186b568551cf50078e5eeda05e3953 on spyder-ide:master.

[zjp]

Sorry it's taken me so long to update this PR. It looks like the last remaining failure is in PyQt5 on Python 3.7/Windows/Conda. The version in the runner is 5.9.2, but the last version available on Conda for that platform/tool combination is 5.15.7 so it would be possible to use almost the same version as the non-Conda version (5.15.10). Let me know your thoughts.

[zjp]

I found a workaround.