Public SavedObjectsClient.resolve fails when batching sometimes

[jportner]

Kibana version: 7.16 (unreleased)

Describe the bug:

Starting in #112025, the public SavedObjectsClient (SOC) batches individual resolve requests into a single bulkResolve.
We discovered a bug in #113160 where the batched resolve results would not be mapped correctly in the case of "aliasMatch" outcomes.

In fixing that bug, I introduced a new bug that caused batched resolve requests to sometimes return an undefined response, because the request array indices were not properly aligned with the response array 😱

Steps to reproduce:

1. Add some code that triggers three resolve requests in quick succession: type/1, type/1, type/2.
2. A single bulkResolve HTTP request will be made for [type/id, type/other-id]
3. The first two requests will return as expected, but the third will return undefined

Expected behavior: All requests should return the appropriate result

Any additional context:

Existing unit tests are in place and partially exercise deduplication.
As long as the duplicate request is at the end, it doesn't cause any problems.

E.g., three resolve requests like this works fine today: type/1, type/2, type/1.

So the fix should exercise this in tests: type/1, type/2, type/1, type/3.
That will ensure that requests are deduplicated in the batched bulkResolve, and that other requests both inside the array and at the end of the array still work as expected.

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)