Hovered areas should come-to-front

[nickofthyme]

Is your feature request related to a problem? Please describe.
No, just inconsistent UI

Describe the solution you'd like
When I hover over a given series in the legend, all other series opacity is reduced. However when areas are overlapping each other, the top-level series (aka rendered last) are coving the selected series and opac like seen below..

Notice the green series is active but being covered by the top red series.

Ideally, it would render the selected green series above/after all others. Just like it looks when the top red series is active like below...

Should also include points

Describe alternatives you've considered
None that I can think of

Additional context
Related to recently fixed render ordering bug #287

Checklist

• this request is checked against already exist requests
• every related Kibana issue is listed under Kibana Cross Issues list
• kibana cross issue tag is associated to the issue if any kibana cross issue is present

[nickofthyme]

@cchaos let me know if this is intended behavior.

[cchaos]

Makes sense to me @nickofthyme !