Improve handling of Windows path change in Python 3.8+

In PR #1759 we made a fix to try and solve problems caused by the change in library path behavior of Python >= 3.8 on Windows. Following the solution used in OIIO, we basically defaulted to adopting the previous Python behavior. However, based on feedback in PR #1668, this should be improved.

There is not agreement that the solution is simply to make the existing env var default to the Python 3.8+ behavior since the people most likely to be affected by the problem are users with limited development expertise.

Based on TSC discussion, we will investigate building the Python binding statically, similar to the wheels. At that point we would remove the OCIO_PYTHON_LOAD_DLLS_FROM_PATH env var option. Users would need to manage the paths on their own.

Another solution would be to add only the path(s) where the OCIO required libraries are, although initial discussion suggested this might be more difficult to get right.

We're open to feedback on the best approach. The recommended solution might be something that should be coordinated among ASWF projects, as it's likely that many of them are experiencing this issue.

For reference, here was the OIIO discussion on this topic:
https://github.com/OpenImageIO/oiio/pull/3470
And here was the USD approach:
https://github.com/PixarAnimationStudios/USD/commit/2a6c08f921bc8e58bd3fb9d8cda30a68f76b758a