Respect sizemode='area' when marker.size is a constant

[cpsievert]

When marker.size is a constant, marker.sizemode is currently silently ignored (i.e., it's always set to diameter, regardless of whether the user specified marker.sizemode='area'):

https://codepen.io/cpsievert/pen/zazXgw

At the very least I think this should generate a warning/message. IMO the behavior should change at some point so that marker.sizemode='area' is respected, regardless of whether marker.size is a number or an array -- perhaps an item to add to #420?

[etpinard]

At the very least I think this should generate a warning/message.

Plotly.validate can do that for you: https://codepen.io/etpinard/pen/zazQNP?editors=0010

[gvwilson]

Hi - this issue has been sitting for a while, so as part of our effort to tidy up our public repositories I'm going to close it. If it's still a concern, we'd be grateful if you could open a new issue (with a short reproducible example if appropriate) so that we can add it to our stack. Cheers - @gvwilson