Fix double click legends when groupclick is set to toggleitem

[archmoj]

Fixes #5908.

Before vs After

@plotly/plotly_js

[alexcjohnson]

💃 As discussed, at some point we'd like it to be that the groupclick attr controls what counts as an “item” when you click on something inside a group (a single line in the legend - usually a trace - or the whole group) and then the itemclick and itemdoubleclick attrs both say “does this event toggle that one item, toggle everything else, or do nothing?”

But this is a clear improvement so we can certainly start with this!