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GeoEnum static members are used in constexpr in GeoListId.
Previous code worked because the static members where inside the same translation unit.
This code:
1. Declares the static members to use them as constant expressions with the value
2. Definition of the static members (odr-used) shall not contain an initializer.
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This commit is an independent refactor of the identifications used at Sketcher level.
It introduces a new type "GeoElementId" as a combination of GeoId and PointPos.
It moves the Undefined GeoId, previous Constraint::GeoUndef to GeoEnum, together with all
other fixed values of GeoIds.
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Separate struct into own file to avoid having to include all the dependencies of SketchObject in other code that relies on GeoEnum.
