Large preloaded JSON was stored inside an HTML attribute. Because JSON
contains quotation marks that could end the attribute early, Rails had
to convert those characters into HTML-safe text. Processing every
character made the response larger and slower to generate.
This change places the preloaded JSON in a non-executable
`application/json` script element and reads it from the element's text
content.
On a site with 11K categories, the escaping was showing up as a hotspot where we spend ~400ms escaping the massive preloaded JSON.