Remove duplicate entry from search results

[HiroyasuNishiyama]

The search results sometimes contain two identical entries, one with the snippet and another without it.
This is because index search results and title search results are treated separately.
This PR attempts to remove the duplicate results.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.

Project coverage is 37.16%. Comparing base (9093134) to head (04f73e6).

Files with missing lines	Patch %	Lines
SwiftUI/Model/SearchOperation/SearchOperation.mm	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #979      +/-   ##
==========================================
- Coverage   37.23%   37.16%   -0.08%     
==========================================
  Files         111      111              
  Lines        6346     6358      +12     
==========================================
  Hits         2363     2363              
- Misses       3983     3995      +12     

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[BPerlakiH]

Thank you @HiroyasuNishiyama for bringing this up. I am looking into it, how it could be handled the most performant way.

[BPerlakiH]

@HiroyasuNishiyama Please see my proposition of solving this here: #981

[kelson42]

Superseeded by #981