Migrate recursive reverse string method and tests to ReverseString

[ai-nihar]

• Moved recursive reverse method from ReverseStringRecursive.java to ReverseString.java
• Moved tests from ReverseStringRecursiveTest.java to ReverseStringTest.java
• Deleted old ReverseStringRecursive files

• 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 75.11%. Comparing base (e78d53d) to head (511daff).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6504      +/-   ##
============================================
+ Coverage     75.09%   75.11%   +0.02%     
- Complexity     5569     5571       +2     
============================================
  Files           686      685       -1     
  Lines         19307    19307              
  Branches       3732     3732              
============================================
+ Hits          14498    14502       +4     
+ Misses         4245     4244       -1     
+ Partials        564      561       -3     

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