feat: Add "Copy Code" button to code blocks in documentation

[GaneshPatil7517]

Summary

This PR implements the "Copy Code" feature requested in issue #7698.
A Copy button is added to the top-right corner of each code block on the documentation site, allowing users to copy the entire code snippet with a single click.

Motivation

Currently, users must manually select and copy code from documentation pages.
This is time-consuming, error-prone, and difficult on mobile devices.

Adding a Copy button:

• Improves developer experience
• Makes code examples easier to use
• Reduces friction while following documentation
• Aligns Webpack docs with modern documentation standards (e.g., MDN, Next.js, TailwindCSS)

Implementation Details

• Added new CodeBlock component with a built-in Copy button.
• Integrated navigator.clipboard.writeText() to copy code.
• Styled the button to match Webpack documentation UI.
• Updated mdx-components.js to use the new CodeBlock wrapper.
• Ensured accessibility (focus, hover states).

Screenshots / Demo

(If you want, add before/after screenshots here)

Linked Issue

Closes #7698

Checklist

• Copy Code button added
• Works on desktop & mobile
• No breaking changes
• Code formatted and linted

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[evenstensberg]

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