Fix issue in HashingStoredFieldVisitor with stored fields

[cwperks]

Description

This PR fixes a bug inside HashingStoredFieldVisitor to account for stored_fields which are stored separately from _source in the backing index. This PR also adds integ tests to verify the correct behavior.

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)

Bug fix

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 70.89%. Comparing base (703d40f) to head (c4722a4).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
...security/configuration/DlsFlsFilterLeafReader.java	50.00%	1 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4826      +/-   ##
==========================================
- Coverage   70.99%   70.89%   -0.10%     
==========================================
  Files         310      310              
  Lines       20938    20946       +8     
  Branches     3326     3331       +5     
==========================================
- Hits        14865    14850      -15     
- Misses       4325     4344      +19     
- Partials     1748     1752       +4     

Files with missing lines	Coverage Δ
...security/configuration/DlsFlsFilterLeafReader.java	62.09% <50.00%> (-0.23%)	⬇️

... and 6 files with indirect coverage changes