Add dragmode: false

[jonfunkhouser]

This PR adds the dragmode: false functionality mentioned in #2844 (comment)

I added an example chart with this setting to my existing sample, so this can be previewed on mobile devices: https://jonfunkhouser.github.io/plotly-mobile/

[etpinard]

Thanks very much for this PR and let me apologize for the delayed response (our 1.42.0 release cycle was a little hectic).

Could you confirm that hover still works when dragmode: false?

[jonfunkhouser]

Sorry, I was away last week. Yes, hover still works in dragMode: false. I updated the sample site to include plotly_hover debug output.

[etpinard]

Thanks @jonfunkhouser !

I wonder if we could do better. By dragging we effectively halt hover and the hover labels (if any) remain in place. Maybe instead we could treat mouse "drag" as a mouse "move" under dragmode: false. But that might make things too confusing though.

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Regardless, we'll need to add a test to 🔒 down the hover on dragmode: false behavior. @jonfunkhouser would you be interested?

[jonfunkhouser]

Yes, I'll add a test for that case. I'll also investigate your suggestion, it makes a lot of sense.

[etpinard]

Brilliant PR, this will be part of our next minor release.