[spec] MathJax and search / c&p on page

For example, try searching for the text 0x00 on the page https://webassembly.github.io/spec/core/binary/instructions.html. In Safari, that string is "Not found" -- in Chrome, there are seven results, but the correct result is never indicated using the normal selection highlight, and the browser doesn't even scroll to the right point for all the results. Attempting to select the text 0x00 doesn't work at all in Chrome. In Safari, attempting to select text does something difficult for me to describe other than that it's "slightly cursed".

Anyone working directly with WebAssembly will be paging through these documents constantly, so it would be helpful for them to support basic browser text operations. Or, at least, I've personally been annoyed by these issues enough to file this issue, and I'm sure I'm not the only one!

Reproduce the search and selection problems for “0x00” on https://webassembly.github.io/spec/core/binary/instructions.html in Safari and Chrome. Investigate how this specification page is generated and rendered; done means browser find, scrolling, selection, and copy operations work normally in both browsers.