Q_ENUMS is deprecated

[jbellister-slac]

Was poking around Qt6 a bit and this was the most obvious problem. The way we add enums to get them to show up in Qt designer is currently through use of Q_ENUMS. This is deprecated in PyQt5 and removed entirely in both PyQt6 and PySide6.

The new way is as described here: https://www.riverbankcomputing.com/static/Docs/PyQt6/metaobjects.html#pyqtenum

Will need to do this in a backwards compatible way though.

As a side note PyQt6 also dropped support for unscoped enums (and PySide6 discourages their use). QtPy makes this not an issue (for now at least) but there are automated scripts out there for updating if we do need to at some point.