[Lens] Handle mixed datatypes on the X axis better (i.e. date field and string field)

[wylieconlon]

Because Lens supports layers, users can mix data on the X axis and get confusing results. Because this is confusing, we need to find a solution. Some options might be:

• Throw an error
• Display multiple charts instead of only one
• Hide data if it's not the right type

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[wylieconlon]

Looked into this a bit, and it seems like we should be throwing an error at rendering time if this is configured. It's the best way to indicate to the user that they are doing something wrong.

[markov00]

You can see this as a feature in specific cases:

• when you are displaying categorical data from two different indices it's fine to have the x values mixed, usually, we render each set of x values (if they differ) one aside of the other

The only thing is missing is a way to sort in elastic-charts these values, we are going to add this feature, hopefully soon

[flash1293]

We handle this nicely now, respecting formatting in the cases where mixing works fine (e.g. terms and filters) and throwing an error for ugly cases (e.g. date histogram + number histogram)