Fix Unified highlighter for nested fields when using matchPhrasePrefixQuery

[sjs004]

Description

CustomUnifiedHighlighter.rewriteCustomQuery() wasn't handling nested query (internally written as OpenSearchToParentBlockJoinQuery). Therefore unified highlighter wasn't working. Added the missing handling & updated tests

Related Issues

Resolves #19106

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for d61fbdb: FAILURE

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 result for 17794cc: FAILURE

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 result for 739a4b9: UNSTABLE

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

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.01%. Comparing base (83b2a6d) to head (739a4b9).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
...ne/search/uhighlight/CustomUnifiedHighlighter.java	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #19442      +/-   ##
============================================
+ Coverage     72.93%   73.01%   +0.07%     
- Complexity    70236    70288      +52     
============================================
  Files          5700     5700              
  Lines        322150   322152       +2     
  Branches      46616    46617       +1     
============================================
+ Hits         234966   235206     +240     
+ Misses        68225    67955     -270     
- Partials      18959    18991      +32     

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[sjs004]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review. ✅ Project coverage is 73.01%. Comparing base (83b2a6d) to head (739a4b9). ⚠️ Report is 9 commits behind head on main.

Files with missing lines Patch % Lines
...ne/search/uhighlight/CustomUnifiedHighlighter.java 0.00% 1 Missing and 1 partial ⚠️
Additional details and impacted files

@@             Coverage Diff              @@
##               main   #19442      +/-   ##
============================================
+ Coverage     72.93%   73.01%   +0.07%     
- Complexity    70236    70288      +52     
============================================
  Files          5700     5700              
  Lines        322150   322152       +2     
  Branches      46616    46617       +1     
============================================
+ Hits         234966   235206     +240     
+ Misses        68225    67955     -270     
- Partials      18959    18991      +32     

☔ View full report in Codecov by Sentry. 📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

org.opensearch.search.fetch.subphase.highlight.HighlighterSearchIT.testWithNestedQuery, this test fails if I remove the newly added block & I have debugged also that branch is being covered. Not sure why test report is suggesting that newly added code is not covered. One reason could be that this particular test suite may not be part of coverage report