ItemImportFileTask

`construct.item.import_file`: import a mesh or a tet volume file as an item, so the model can look at it (opal-mesh-references §OMO-1).

In the namespace construct::opal. Declared in src/libs/libconstruct/construct/opal/ItemImportFileTask.hpp.

Detailed description

The counterpart of `construct.item.export_file`, and the Tier 2 composite `scene.import_mesh` of construct-operations. It reads the file through construct::asset::readImportFile, the path the GUI import shares, on the task thread; it adds the items on the main thread as one undo step, as `construct.bake` does. A member of a dropped folder or archive is named by `attachment` and `member`; an archive member is written to the work folder first (§OMD-7).