Refactor: Cleanup for Combination.java

[AbeTheAmatuer]

Just changed class name, variable names and comments to make it more clear and understandable.
-Changed class name from "Combination" to "CombinationGenerator", to make it a bit more accurate.
-Added multiple comments
-Changed variable "n" to "desiredLength" to make the variable name more accurate and clear.
-Updated javadoc tags accordingly

• 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 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 41.43%. Comparing base (ebed8b3) to head (9bc17d8).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5301      +/-   ##
============================================
+ Coverage     41.41%   41.43%   +0.01%     
  Complexity     2551     2551              
============================================
  Files           520      520              
  Lines         15447    15447              
  Branches       2950     2950              
============================================
+ Hits           6398     6400       +2     
+ Misses         8754     8753       -1     
+ Partials        295      294       -1     

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[AbeTheAmatuer]

I made an error one sec