Tooltip : use "represent_value"

[Gustry]

According to previous feedbacks, "represent_value" was not working correctly. We should try and test and use it instead of trying to cover all widgets.

[Gustry]

Note for myself :

layer=iface.activeLayer()
widget = layer.editorWidgetSetup(3)
print(widget.config())
# layer.editorWidgetSetup( 3, QgsEditorWidgetSetup( QStringLiteral( "ValueMap" ), config ) );

[Gustry]

This expression represent_value must be used when generating the HTML table.