Add isgreater() documentation entry for C++

[kentgabmagbuhat-oss]

Description

This pull request adds a new documentation entry for the C++ isgreater() function. The entry explains its purpose, syntax, parameters, return value, key behavior, and provides multiple examples demonstrating its use, including comparisons involving NaN values. This helps learners understand how to safely compare floating-point numbers in C++.

Issue Solved

Closes #7992

Type of Change

Adding a new entry

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issues Solved section.

[CLAassistant]

All committers have signed the CLA.

[mamtawardhani]

Looks good for a second review! 🚀

[dakshdeepHERE]

Did some minor changes here and there, looks good for merge 🚀

[github-actions]

👋 @kentgabmagbuhat-oss
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