Plain-text header, for exports and aria labels.
Prefers ColumnDef.headerName, then a string or numeric header, then falls back to the column id.
header
The column to label.
The header as plain text, or '' if nothing usable was found.
''
Plain-text header, for exports and aria labels.
Prefers ColumnDef.headerName, then a string or numeric
header, then falls back to the column id.