[KQL] Define KqlContext type

[lukasolson]

Summary

When processing KQL DSL into ES query DSL, we make use of a helper object, context. This was introduced when we added support for nested fields, but was never correctly typed. This PR simply introduces the correct type for this object.

Checklist

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility

For maintainers

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

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesSv)

[tsullivan]

LGTM

[kibana-ci]

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Metrics [docs]

Public APIs missing exports

Total count of every type that is part of your API that should be exported but is not. This will cause broken links in the API documentation system. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats exports for more detailed information.

id	before	after	diff
@kbn/es-query	11	12	+1

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

cc @lukasolson