PyEnum: make forgiving duplicates work with Python 3.11

PyEnum: make forgiving duplicates work with Python 3.11

There was a silent change in PyEnums that turns Enum attributes
into properties. This does not harm the Python interface but
needed some change in the duplication emulation.

Furthermore, new internal enums are created with an underscore name.

The meta class was changed from EnumMeta to EnumType.

[ChangeLog][shiboken6] The new Python Enums are now compatible with Python 3.11

Change-Id: I3b1ab63dc5eed15a75ebd0f42dddf4001f640c00
Pick-to: 6.3
Task-number: PYSIDE-1735
Fixes: PYSIDE-1960
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>
(cherry picked from commit da2cf031521815a9559ca784beadb70c7a2852d9)

Gbp-Pq: Name PyEnum-make-forgiving-duplicates-work-with-Python-3.11.patch