[Lens] Switching to xy charts loses all dimensions if not all of them can be mapped

[flash1293]

Kibana version: Probably 7.8

Describe the bug: When switching from another chart type (table or pie/donat) to an xy chart type other than stacked bar and not all dimensions of the current chart can be mapped (e.g. 4 dimensional table with 3 buckets to line chart or 3 layer pie chart to area chart), the complete layer is reset, even if some dimensions could be preserved.

Steps to reproduce:

1. Go to Lens
2. Create a table vis with a bunch of columns
3. Switch to xy chart other than stacked bar
4. Empty chart is shown

Expected behavior:
As many columns as possible should be mapped to the chart dimensions - all others should be dropped.

Screenshots (if relevant):

[elasticmachine]

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

[wylieconlon]

@flash1293 The description of the issue makes it sound like a duplicate of other issues, but the PR you opened looks like it's solving only one specific case. Can you clarify? #72634 and #54943?

[flash1293]

You are right @wylieconlon , it's just about a single case which worked fine previously. I updated the description.