Summary

This PR prepares search source for migration to the new platform and to the new search APIs.

Resolves #44659.
Resolves #44738.

Removal of search request

The SearchRequest module added a lot of complications to the way requests were processed, and included behavior that was never used (like lifecycle events and continueIncomplete). It was a confusing construct that had two different promises that might resolve at any given point but really just represented a success or a failure. This PR removes the SearchRequest class (in addition to RequestStatus and IsRequest) and instead passes the actual Elasticsearch request DSL object directly to the search strategy.

Removal of search request queue

This was really just an array, and was only helpful when courier was destroyed so all current requests could be aborted. Now it's the responsibility of the caller of fetch to abort the request. The array of requests to process can now be found in fetchSoon.

Allow passing abortSignal to searchSource.fetch

This PR removes the previous way for a search source to abort an in-progress request, cancelQueued, in favor of passing an abortSignal to the fetch method. This allows the caller of fetch to more easily control when a request should be aborted, and is in line with how we handle aborting other things (like the interpreter and ES cluster client).

Refactoring of callClient

The callClient module used to do things in a very funky way. It would conditionally respond to requests with either a response, or an ABORTED constant. This caused a lot of conditional handling or requests/responses. Now, instead of responding with disparate values, it will either resolve with the response or reject with an error, which in the case of an aborted request, is an AbortError.

For testers

This PR affects the querying of Elasticsearch in many places that should be tested:

• Discover
  • View surrounding documents
  • View single document
• Visualize
• Dashboard
  • Saved visualizations
  • Saved searches
• Maps
• Rollups

It's also important to test these areas in conjunction with other things that affect the Elasticsearch query, like KQL/Lucene, filters, and time ranges (including auto-refresh intervals).

It also affects the creation of new index patterns, which should also be tested.

Checklist

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• 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
• This includes a feature addition or change that requires a release note and was labeled appropriately