feat: add TopKFrequentWords with deterministic tie-breaking (#7298)

[oleksii-tumanov]

The implementation returns the k most frequent words from an input array.
https://en.wikipedia.org/wiki/Top-k_problem

Files added:

• TopKFrequentWords.java
• TopKFrequentWordsTest.java

Test Case (feature demonstration)
Input:

String[] words = {"the", "day", "is", "sunny", "the", "the", "the", "sunny", "is", "is"};
int k = 4;

Expected output:

["the", "is", "sunny", "day"]

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new algorithms include a corresponding test class that validates their functionality.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.42%. Comparing base (4b04ad4) to head (1a0c104).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7297      +/-   ##
============================================
+ Coverage     79.40%   79.42%   +0.02%     
- Complexity     7054     7062       +8     
============================================
  Files           787      788       +1     
  Lines         23114    23129      +15     
  Branches       4544     4548       +4     
============================================
+ Hits          18354    18371      +17     
+ Misses         4025     4024       -1     
+ Partials        735      734       -1     

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