Added Trapping Rain Water code in java

[maitreepatel1110]

Implemented optimal solution for Trapping Rain Water problem using two-pointer approach with O(n) time complexity and O(1) space complexity. Given detailed explanation of approach with test cases for the given algorithm.

• 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 67.11%. Comparing base (6006025) to head (5a76df4).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5930      +/-   ##
============================================
+ Coverage     67.10%   67.11%   +0.01%     
- Complexity     4560     4561       +1     
============================================
  Files           619      619              
  Lines         17098    17098              
  Branches       3296     3296              
============================================
+ Hits          11474    11476       +2     
+ Misses         5168     5167       -1     
+ Partials        456      455       -1     

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[siriak]

We don't add leetcode problems