Create polyfill for JavaScript

[DanielAsare-ux]

This pull request adds a new documentation file that provides a polyfill for the Array.prototype.includes method in JavaScript. The documentation aims to help developers understand how to implement polyfills for older JavaScript environments that do not natively support certain methods.

Key changes:

• content/javascript/concepts/methods/Polyfill/polyfill.md: Added a detailed guide on creating a polyfill for Array.prototype.includes. The guide includes an introduction to polyfills, the syntax for writing a polyfill, and an example implementation with an explanation.<!--
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Description

• Added polyfill concept for JavaScript
• Editing an existing entry (fixing a typo, bug, issues, etc.)

Issue Solved

Type of Change

• Add a new entry

• Adding a new entry
• Editing an existing entry (fixing a typo, bug, issues, etc.)
• Updating the documentation

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.

[SaviDahegaonkar]

Hey @DanielAsare-ux,
I reviewed your file, and the entry does not follow the style-guide documentation guidelines. Please refer to the documentation and make the changes as soon as possible.

Thanks,
Savi