@Override
	public Enumeration<TableColumn> getColumns() {
		return visibleColumns.toEnumeration();
	}
This method will make sure that there are no existing columns in this model's complete
list of columns (visible and hidden) that have the same <b>table model</b> index as
the given index.  This prevents duplicate columns from being added, since clients of this
class do not know about hidden columns and may thus try to add a column that already
exists, but is hidden.
@param modelIndex The table model index of the column that should be removed
Ghidra/Framework/Docking/src/main/java/docking/widgets/table/GTableColumnModel.java