sip6 converts all enums to python Enums, but ONLY creates
Enums with IntFlags types when the c++ type is an enum class : int.
Accordingly we need to patch back in all the operations which treat
enum values as ints, like |, &, bool, etc.
The long term solution here is to move all our c++ enums to enum
class, but that's not always straightforward and can break API
for plugins if it involves the signature of virtual methods.
This ensures that we correctly apply filters to recent projections
too, eg so that a widget showing only vertical crs will ONLY show
recent VERTICAL crs, not every recent crs.
Cleanup QgsProjectionSelectionWidget to use proper models to
drive the combo box. This removes a bunch of very fragile
logic regarding showing and hiding entries on demand, as it
allows us to move all the filtering logic to a single place
in a QSortFilterProxyModel subclass.
This has a few side benefits:
- The combos now dynamically respond to changes like recent
CRS being used in other places in QGIS
- The widget correctly respects horizontal/vertical crs filters
for all entries, including recent crs
