[data.search] Fix unhandled promise rejections

[lukasolson]

Summary

Resolves https://github.com/elastic/kibana/issues/168957.

It turns out the underlying issue was resolved in https://github.com/elastic/kibana/pull/170041 (unhandled errors when deleting not being handled). However this still left it up to consumers of pollSearch to be 100% sure they weren't leaking unhandled promise rejections. This adds code directly to pollSearch that will handle rejections if they aren't handled in the calling code. It also adds tests to consumers of pollSearch to make sure they don't barf in the case that the cancel function errors.

Checklist

• [x] Unit or functional tests were updated or added to match the most common scenarios

[lukasolson]

/ci

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kibana-ci]

:yellow_heart: Build succeeded, but was flaky

• Buildkite Build
• Commit: 18b4dd430f0c9b25be3327a337202dad73b2516b

Failed CI Steps

• FTR Configs #38

Test Failures

• [job] [logs] FTR Configs #38 / maps app maps loaded from sample data "before all" hook in "maps loaded from sample data"

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
data	417.5KB	417.6KB	+98.0B

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
data	52	54	+2

Total ESLint disabled count

id	before	after	diff
data	54	56	+2

History

• :green_heart: Build #206430 succeeded d723bd4ea87448b2802e33f7b6daef3c4bb62af0
• :yellow_heart: Build #206172 was flaky f0c92529ae29cfbe7d48fd5b70c6ae0c808bc560

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

cc @lukasolson