Bug 181121 Model should provide utility method for cube to get correspond dimension key.
In model cube handle, the relation of cube data set and dimension data sets are managed by a series of dimension condition handles.We need model to add utility method so that we can easily get corresponding dimension data set column names according to given cube dimension keys.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/parser/StructureState.java
catch ( InstantiationException e )
		{
			assert false;
		}
		catch ( IllegalAccessException e )
		{
			assert false;
		}
		return struct;
	}
	/**
	 * Populates the dictionary for the structure class and name mapping.
	 * 
	 */
	private static void populateStructDict( )
	{
		assert structDict == null;
		structDict = new HashMap( );
		structDict.put( Action.ACTION_STRUCT.toLowerCase( ), Action.class );
		structDict.put( ColumnHint.COLUMN_HINT_STRUCT.toLowerCase( ),
				ColumnHint.class );
		structDict.put( ComputedColumn.COMPUTED_COLUMN_STRUCT.toLowerCase( ),
				ComputedColumn.class );
		structDict.put( ConfigVariable.CONFIG_VAR_STRUCT.toLowerCase( ),
				ConfigVariable.class );
		structDict.put( CustomColor.CUSTOM_COLOR_STRUCT.toLowerCase( ),
				CustomColor.class );
		structDict.put( EmbeddedImage.EMBEDDED_IMAGE_STRUCT.toLowerCase( ),
				EmbeddedImage.class );
		structDict.put( FilterCondition.FILTER_COND_STRUCT.toLowerCase( ),