Prevent mix up of legend/label selection, refs #8891 and #8851

Make sure the target of new SelectionMoveResizer is the actual legend/label being clicked.
Avoid warning: unused parameter, re #8891 and #8851
Avoid MSVC warning about comment tags, re #8419
Merge remote-tracking branch 'origin/bugfix/8891_2d_plot_label_issues'