fix(a11y): add aria-labels to copy-to-clipboard buttons

[yogeshwaran-c]

Description

The copy-to-clipboard buttons across the UI used empty <button/> elements with no accessible name, making them invisible to screen readers and failing WCAG 2.1 Success Criterion 4.1.2 (Name, Role, Value).

This adds descriptive aria-label attributes to three copy-to-clipboard buttons:

1. curl.jsx - cURL command copy button: "Copy cURL command to clipboard"
2. HighlightCode.jsx - Code block copy button: "Copy to clipboard"
3. request-snippets.jsx - Request snippet copy button: "Copy code snippet to clipboard"

Motivation and Context

Partially addresses #10699

Screen reader users could not identify or interact with these buttons because they had no accessible name. The buttons were rendered as empty <button/> elements inside the react-copy-to-clipboard wrapper.

How Has This Been Tested?

• Verified the buttons render with the correct aria-label attributes
• The react-copy-to-clipboard component passes through props to the child element, so aria-label on the button element works correctly

Screenshots (if appropriate):

N/A - accessibility improvement, no visual change

Checklist

My PR contains...

• No code changes (src/ is unmodified: changes to documentation, CI, metadata, etc.)
• Dependency changes (any modification to dependencies in package.json)
• Bug fixes (non-breaking change which fixes an issue)
• Improvements (misc. changes to existing features)
• Features (non-breaking change which adds functionality)

My changes...

• are breaking changes to a public API (config options, System API, major UI change, etc).
• are breaking changes to a private API (Redux, component props, utility functions, etc.).
• are breaking changes to a developer API (npm script behavior changes, new dev system dependencies, etc).
• are not breaking changes.

Documentation

• My changes do not require a change to the project documentation.
• My changes require a change to the project documentation.
• If yes to above: I have updated the documentation accordingly.

Automated tests

• My changes can not or do not need to be tested.
• My changes can and should be tested by unit and/or integration tests.
• If yes to above: I have added tests to cover my changes.
• If yes to above: I have taken care to cover edge cases in my tests.
• All new and existing tests passed.