Avoid JS syntax errors when visiting our site from our browser

[pavpanchekha]

This PR rewrites the JavaScript files book.js and feedback.js so that they don't raise errors in our own browser. That involved:

• Rewrite let, for of, and arrow functions into old-school JavaScript
• Use IIFEs for callbacks in loops, just like we did in the 00s
• Test for the existence of window, window.addEventListener, and document.addEventListener before using them
• Only loosely related, but also update the patcher to work in Python 3.13

[chrishtr]

I assume you've tested all the browser versions and the website's features?

[pavpanchekha]

Yes