Pagination, phase 1: Add unit tests for :opensearch module with coverage.

[Yury-Fridlyand]

Add unit tests for :opensearch module with coverage. Uncovered: toCursor, because it is will be changed soon. Merge target: #226

Description

Completely pass :opensearch:checkstyleTest. Partial pass for :opensearch:test :opensearch:jacocoTestReport :opensearch:jacocoTestCoverageVerification:

* What went wrong:
Execution failed for task ':opensearch:jacocoTestCoverageVerification'.
> Rule violated for class org.opensearch.sql.opensearch.executor.protector.ResourceMonitorPlan: lines covered ratio is 0.9, but expected minimum is 1.0
  Rule violated for class org.opensearch.sql.opensearch.storage.scan.OpenSearchPagedIndexScan: lines covered ratio is 0.8, but expected minimum is 1.0
  Rule violated for class org.opensearch.sql.opensearch.storage.scan.OpenSearchPagedIndexScan: branches covered ratio is 0.3, but expected minimum is 1.0
  Rule violated for class org.opensearch.sql.opensearch.request.OpenSearchScrollRequest: lines covered ratio is 0.9, but expected minimum is 1.0
  Rule violated for class org.opensearch.sql.opensearch.request.OpenSearchScrollRequest: branches covered ratio is 0.8, but expected minimum is 1.0
  Rule violated for class org.opensearch.sql.opensearch.request.OpenSearchRequest: lines covered ratio is 0.0, but expected minimum is 1.0

Notes:

1. pushDownOffset removed, because it is not used
2. Few files moved to keep file structure consistent

Issues Resolved

N/A

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Merging #233 (3fbcbae) into dev-pagination-v2_revC (a3ef2bf) will increase coverage by 0.77%.
The diff coverage is 100.00%.

@@                     Coverage Diff                      @@
##             dev-pagination-v2_revC     #233      +/-   ##
============================================================
+ Coverage                     95.12%   95.89%   +0.77%     
- Complexity                     3700     3728      +28     
============================================================
  Files                           359      359              
  Lines                          9420     9412       -8     
  Branches                        612      612              
============================================================
+ Hits                           8961     9026      +65     
+ Misses                          443      370      -73     
  Partials                         16       16              

Flag	Coverage Δ
sql-engine	95.89% <100.00%> (+0.77%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...a/org/opensearch/sql/planner/PaginateOperator.java	0.00% <ø> (ø)
.../opensearch/sql/storage/read/TableScanBuilder.java	100.00% <ø> (+10.00%)	⬆️
...sql/opensearch/request/OpenSearchQueryRequest.java	100.00% <ø> (ø)
...l/opensearch/request/OpenSearchRequestBuilder.java	100.00% <ø> (ø)
...ensearch/request/SubsequentPageRequestBuilder.java	100.00% <ø> (ø)
...ql/opensearch/storage/OpenSearchStorageEngine.java	100.00% <ø> (+57.14%)	⬆️
...l/opensearch/storage/scan/OpenSearchIndexScan.java	100.00% <ø> (ø)
...ge/scan/OpenSearchIndexScanAggregationBuilder.java	100.00% <ø> (ø)
...earch/storage/scan/OpenSearchIndexScanBuilder.java	100.00% <ø> (+7.69%)	⬆️
.../storage/scan/OpenSearchIndexScanQueryBuilder.java	100.00% <ø> (+5.88%)	⬆️
... and 13 more

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