[Lens] support legendStats along with valuesInLegend in preparation for legend statistics

[mbondyra]

Summary

This PR addresses phase one of #181035.

Doesn't introduce any user facing changes.
It starts supporting a new saved object property legendStats while supporting a old valuesInLegend property. In this PR, legendStats: ['values'] and valuesInLegend:true are treated as equal. When loading the saved object, valuesInLegend:true is transformed to legendStats:['values']. After loading the document, the Lens app logic is built around the new legendStats property.
When user saves the saved object, we do a reverse operation- we save the runtime state legendStats:['values'] as valuesInLegend: true to ensure backwards compatibility.

Changes for runtime state:

• For xyCharts, the valuesInLegend?: boolean property is replaced with a more extensible legend.legendStats?: LegendStats[] interface

• For partition charts, the showValuesInLegend?: boolean property is replaced with legendStats?: LegendStats[].

after loading - in initialize function:

export function convertToRuntime(
  state: XYPersistedState,
  annotationGroups?: AnnotationGroups,
  references?: SavedObjectReference[]
) {
  const outputState = needsInjectReferences(state)
    ? injectReferences(state, annotationGroups, references)
    : state;
  if ('valuesInLegend' in outputState) {
    return convertToLegendStats(outputState);
  }
  return outputState;
}

before saving :

export function convertToPersistable(state: XYState) {
  const persistableState: XYPersistedState = convertToValuesInLegend(state);
  /.../
}

In the future the legendStats prop would contain also other types of stats -see the issue.

[elasticmachine]

Pinging @elastic/kibana-visualizations (Team:Visualizations)

[cauemarcondes]

Obs Ux Infra changes LGTM.

@mbondyra We are passed FF, should this be targeted to 8.15 instead?

[elasticmachine]

Pinging @elastic/obs-ux-infra_services-team (Team:obs-ux-infra_services)

[dej611]

Done a first code review pass. Left some comments.
Will check locally in a bit...

[nickofthyme]

Looks good overall. I just have some ideas on how to support future migrations we want to add. Using some kind of pass-through migration, similar to flow, that migrates something and passes it to the next migration. Both converting to and from persitableState, while avoiding multiple deep clones of the state.

[kibana-ci]

💚 Build Succeeded

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• Commit: 58e2f97
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Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
lens	1405	1407	+2

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
expressionXY	167	166	-1
lens	569	567	-2
visualizations	831	832	+1
total			-2

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
expressionPartitionVis	36.4KB	36.5KB	+57.0B
expressionXY	128.4KB	128.5KB	+60.0B
lens	1.4MB	1.4MB	+974.0B
observability	287.3KB	287.3KB	+5.0B
observabilityAIAssistantApp	151.1KB	151.1KB	+5.0B
ux	169.8KB	169.9KB	+93.0B
visTypePie	11.2KB	11.3KB	+80.0B
visTypeXy	42.2KB	42.3KB	+35.0B
total			+1.3KB

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
expressionPartitionVis	26.7KB	26.6KB	-13.0B
expressionXY	38.8KB	38.9KB	+90.0B
visTypePie	8.4KB	8.5KB	+154.0B
visTypeXy	28.5KB	28.7KB	+182.0B
visualizations	58.9KB	59.0KB	+94.0B
total			+507.0B

Unknown metric groups

API count

id	before	after	diff
lens	670	669	-1
visualizations	862	863	+1
total			-0

References to deprecated APIs

id	before	after	diff
lens	113	114	+1

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[dej611]

Tested locally and it works great! 🥳