[Lens] Improve suggestions for multiple layers

[flash1293]

We don't currently have logic that builds good query suggestions for multiple layers. It's not a good suggestion to remove a split on one layer, but not the other.

Instead, the only suggestions that should be shown when the user has multiple layers are "Same query, different chart type". For example, "Stack all layers"

[elasticmachine]

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

[wylieconlon]

@flash1293 I'm not sure I understand the issue, my guess is that the note which we originally wrote in the Lens board has gotten out of date.

Currently, when we have multiple layers, we generate the following suggestions:

1. For each layer, remove all other layers
2. If the chart is an unstacked bar chart, then we suggest:
   • Stacking all layers
   • Using a line chart for all layers
3. If the chart is a stacked bar chart, we suggest:
   • Using an unstacked bar chart
   • Using a line chart

I think these suggestions are reasonable, so I'd like to close this issue.

[flash1293]

You are right, I wasn't sure about the history.