[origin] legend not properly read

Requirements

• I searched through the issues if the issue already exists

Steps to reproduce

Import the filetwo_layers_as_two_coordinate_systems_with_legend.opj (also available in tests/import_export/Project/data/).

Expected

The legend in the Origin project is imported as a CartesianPlotLegend.

Observed

The legend in the Origin project is imported as TextLabel.

Origin's 'Legend' is a special text label with special notation:

• https://www.originlab.com/doc/origin-help/legend-colorscale
• https://www.originlab.com/doc/en/LabTalk/ref/Legend-Substitution-Notation

Inside the opj file it is stored as an Annotation-element in the Annotation-list of a Layer-element.

For other test projects that we have (for example2_spektrum-Statistik.OPJ created with Origin7 or Figure_19_beispiel.opj created with Origin9.85 the legends are properly imported