Add Infix to Postfix conversion implementation

[laiba-Ashfaq]

Fix #6655
Infix Expression: Operator is between operands → A + B

Postfix Expression: Operator is after operands → A B +

We use a stack to temporarily hold operators and handle operator precedence.

• 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

[DenizAltunkapan]

@laiba-Ashfaq Please fix the failing workflows so I can start the review.

[github-actions]

This pull request has been automatically closed because its workflows or checks failed and it has been inactive for more than 14 days. Please fix the workflows and reopen if you'd like to continue. Merging from main/master alone does not count as activity.