[Backport 2.x] [Refactor] Refactors remaining ImmutableOpenMap usage to j.u.Map (#7309)

[nknize]

Backport d984f50 from #7309.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18571/
• CommitID: 7aeebbf
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18578/
• CommitID: 7aeebbf
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18590/
• CommitID: 7aeebbf
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[nknize]

Okay, this is beyond ridiculous. These same BWC and Segrep w/ remote store tests keep failing. We need to either mute or fix them as the time loss has far surpassed unreasonable.

[nknize]

I was able to periodically repro the Yaml test failures. Looks like there's an occasional java.net.ConnectException: Connection refused. Many of these instances occur from adminClient().performRequest(request); called from ensureNoInitializingShards(); I'm not sure this is specific to this call, though. Possibly we're running out of connections based on the cluster config?

Will keep digging.

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/18813/
• CommitID: 0ad7ad3
  Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green.
  Is the failure a flaky test unrelated to your change?

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      2 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString

• URL: https://build.ci.opensearch.org/job/gradle-check/18816/
• CommitID: 0ad7ad3
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Merging #8316 (0ad7ad3) into 2.x (04ec607) will decrease coverage by 0.02%.
The diff coverage is 91.48%.

@@             Coverage Diff              @@
##                2.x    #8316      +/-   ##
============================================
- Coverage     70.69%   70.68%   -0.02%     
- Complexity    56900    56901       +1     
============================================
  Files          4714     4713       -1     
  Lines        269657   269540     -117     
  Branches      39863    39856       -7     
============================================
- Hits         190640   190511     -129     
- Misses        62611    62684      +73     
+ Partials      16406    16345      -61     

Impacted Files	Coverage Δ
...cluster/reroute/TransportClusterRerouteAction.java	44.73% <0.00%> (+0.58%)	⬆️
...ices/shards/TransportIndicesShardStoresAction.java	4.90% <0.00%> (ø)
...a/org/opensearch/common/io/stream/StreamInput.java	88.60% <ø> (-1.32%)	⬇️
.../org/opensearch/common/io/stream/StreamOutput.java	94.81% <ø> (-0.38%)	⬇️
.../src/main/java/org/opensearch/gateway/Gateway.java	8.33% <0.00%> (ø)
.../opensearch/rest/action/cat/RestIndicesAction.java	45.77% <0.00%> (-0.12%)	⬇️
...min/indices/shards/IndicesShardStoresResponse.java	53.19% <71.42%> (+1.41%)	⬆️
...dmin/indices/settings/get/GetSettingsResponse.java	74.39% <91.66%> (-0.61%)	⬇️
.../java/org/opensearch/index/mapper/FieldMapper.java	80.75% <94.11%> (+0.01%)	⬆️
...va/org/opensearch/cluster/node/DiscoveryNodes.java	87.62% <97.43%> (-1.60%)	⬇️
... and 18 more

... and 429 files with indirect coverage changes