[Lens] Regular bar chart stacked on histogram x axis when using multiple layers

[flash1293]

Kibana version: master

Describe the bug: When a Lens chart has more than one layer with a histogram x axis, then bars are stacked even if non-stacked bar chart is selected. This is happening because enableHistogramMode is set to true.

Steps to reproduce:

Expected behavior:
The bars should not be stacked

Any additional context:
Our logic for enabling histogram mode is this: isHistogram && (seriesType.includes('stacked') || !splitAccessor):
https://github.com/flash1293/kibana/blob/bbda3f99ef0d9780bcf1b9af88d26e3cc04e316e/x-pack/plugins/lens/public/xy_visualization/xy_expression.tsx#L448

If series has histogram x axis and is either of a stacked type or doesn't have a "break down" dimension, use histogram mode

This logic is missing the multiple layer case and the multiple metric case - in both cases we can't use histogram mode. The logic should be extended.

[elasticmachine]

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

[PavithraCP]

Hello @flash1293, I'm interested in picking this issue. Please let me know if this is still available.

[flash1293]

@PavithraCP I assigned you to the issue, let me know when you have questions

[PavithraCP]

@flash1293 I've raised a PR https://github.com/elastic/kibana/pull/78525/files for this issue. I've added the logic to not enable histogram mode for multiple layer case. The issue description states that we need to disable histogram mode for multiple metrics case too. However, I couldn't quite understand what multiple metrics would translate to in the code. My initial guess is that it's related to the xScaleType parameter, please lmk if this sounds right.

[wylieconlon]

Closed by #78525