OHLC calculations are off on category axes

[etpinard]

See https://codepen.io/plotly/pen/KXwaMR

cc @cldougl

[alexcjohnson]

oof, I hate to say it but I'm not sure we have a good way to do this within the current framework. You simply can't have data points on a category axis that don't point to exact categories. So the options I see are:

• build some sort of shim into scatter to allow shifting points away from their data values (cf Add Jitter to Scatterplot-Points #299)
• build a hook to allow transforms to alter gd.calcdata after it's been created
• rebuild OHLC as a native trace without transforms

Am I missing some simpler option?

[cldougl]

This issue originally came up from someone trying to workaround a scenario similar to #1382 and remove gaps caused by weekends/missing dates. Not setting x (to use default linear coordinates) and then using ticktext works well as a workaround to using category.