IgxGridToolbarExporter - Field name instead of header caption is exported to csv if a column is grouped

[mkamiishi]

Description

When a grouped column is exported to csv, field name instead of header caption is exported.

• igniteui-angular version: 20.1.7
• browser: Chrome

Steps to reproduce

1. Go to the sample https://stackblitz.com/edit/nh7upksw-ycvuptt9?file=src%2Fapp%2Fgrid%2Fmulti-column-headers-export%2Fmulti-column-headers-export.component.html
2. Click "EXPORT" button on the top right corner and select "Export to CSV" from the dropdown.
3. Observe the exported csv file.

Result

Field names are exported as headers for grouped columns.

Expected result

Header captions should be exported.