Add Dijkstra Algorithm Implementation Using PriorityQueue (Fixes #7112)

[prasanth-30011]

Summary

This Pull Request adds a clean and efficient implementation of Dijkstra’s Algorithm using a PriorityQueue, as requested in issue #7112.

What This PR Includes

• New file Dijkstra.java inside the appropriate package.
• Implementation of Dijkstra’s shortest-path algorithm using:
  • Adjacency list representation
  • Min-heap (PriorityQueue)
• Detection and handling of negative weighted edges (throws exception, as required).
• Code follows the structure, style, and formatting used throughout the TheAlgorithms/Java repository.

Why This Change Is Needed

The project did not previously include a fully correct and optimized Dijkstra implementation using a PriorityQueue.
This PR fills that gap and matches the algorithm request posted under issue #7112.

Related Issue

Fixes #7112