Collapse example code blocks in challenge descriptions

[jhong66]

Checklist:

• I have read and followed the contribution guidelines.
• I have read and followed the how to open a pull request guide.
• My pull request targets the main branch of freeCodeCamp.
• I have tested these changes either locally on my machine, or GitPod.

We added a dropdown toggle button to all example code blocks on the https://www.freecodecamp.org/learn courses. This aims to make dealing with large code examples
less awkward for the user. Here is an example:

Toggled on (default state):

Toggled off:

Closes freeCodeCamp#54190