refactor: cleanup AhoCorasick

[alxkm]

Change ArrayList to List, which provides more flexibility.
Removing redundant type in generics.

• 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 45.86%. Comparing base (8a89b42) to head (01cb54a).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5358      +/-   ##
============================================
- Coverage     45.88%   45.86%   -0.02%     
+ Complexity     2857     2856       -1     
============================================
  Files           525      525              
  Lines         15420    15418       -2     
  Branches       2917     2917              
============================================
- Hits           7076     7072       -4     
- Misses         8048     8049       +1     
- Partials        296      297       +1     

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