[Expressions] Partial results example plugin

[dokmic]

Summary

Resolves #108682.

This PR also changes the mapColumn function implementation to support partial results.

At first, the idea was to emit table rows gradually upon expression resolution, but it affects the performance significantly. The implementation using merge will emit the number of values equals to the rows number. Using all possible optimizations, the duration was tripled on the demo data (about 3000 rows), which was unacceptably slow.

In the result, the best solution was to use combineLatest and wait until the expression emits at least one value for every row. That doesn't affect the performance of the function and adds support of the partial results if the underlying expression emits multiple values.

Checklist

• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[ppisljar]

LGTM

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 882b437
• Storybooks Preview

Metrics [docs]

Page load bundle

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

id	before	after	diff
expressions	128.3KB	128.3KB	-1.0B

History

• 💚 Build #155402 succeeded 869e3d120f7ea881a8b394996cad8ee94d8fe8a1
• 💔 Build #155394 failed fcee671b86d016b0a5f188e8d7241f1ed117897d

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