Is your feature request related to a problem? Please describe.
Currently, the legend items capture the mouse only when hovering over the bounding box of the legend item ink:

• this causes flashing when the mouse moves from one item to the next
• the indentation in the nested legend case also leads to flashing

Describe the solution you'd like
The entire legend row should be active, such that the

• width use is maximized (100%) for capture, even if a legend item is indented, or one text is shorter than on other lines
• height is also maximized, so there's no gap between rows

Describe alternatives you've considered
None

Additional context
These help not just with flash avoidance but also, easier and more predictable activation by the user and better Fitts law adherence.

If accepted, this could be added to #858

Kibana Cross Issues
Not aware

Checklist

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• every related Kibana issue is listed under Kibana Cross Issues list
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