Added a Simple XOR Cipher

[lcsjunior]

I've transcribed one of my simple XOR ciphers that I use into Java with the intention of participating in Hacktoberfest and future contributions. Please consider accepting my code.

This is a simple implementation of the XOR cipher that, given a key, allows you to encrypt and decrypt plaintext.

• 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 53.00%. Comparing base (66ee59c) to head (d98740c).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5490      +/-   ##
============================================
+ Coverage     52.98%   53.00%   +0.01%     
- Complexity     3311     3314       +3     
============================================
  Files           529      530       +1     
  Lines         15343    15356      +13     
  Branches       2925     2926       +1     
============================================
+ Hits           8130     8139       +9     
- Misses         6880     6881       +1     
- Partials        333      336       +3     

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[siriak]

Looks good, thanks!