Adding ElasticCollision2D

[the-yash-rajput]

• 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

❌ Patch coverage is 93.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.85%. Comparing base (b312567) to head (aabd6a4).

Files with missing lines	Patch %	Lines
.../com/thealgorithms/physics/ElasticCollision2D.java	93.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6802      +/-   ##
============================================
+ Coverage     77.84%   77.85%   +0.01%     
- Complexity     6394     6397       +3     
============================================
  Files           733      734       +1     
  Lines         21333    21363      +30     
  Branches       4183     4185       +2     
============================================
+ Hits          16607    16633      +26     
- Misses         4058     4061       +3     
- Partials        668      669       +1     

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[the-yash-rajput]

@alxkm Please review and merge this PR.