Improve tabset init

[liamcmitchell]

Tabset init was responsible for a lot of the page load time, mostly due to layout thrashing.

• Split init into read and mutate phases, avoiding layout-read-mutate loops
• Implement tabs in vanilla JS, avoiding DOM -> string -> DOM conversion in handlebars
• Refactor event handling, removing need for state vars per tabset and closures per tab

Before

../formatters/html/dist/html-IOQDFYUW.js                             148.6kb

After

../formatters/html/dist/html-KG3N33ZC.js                             144.8kb

[josevalim]

Fantastic. Btw, I assume if there are no tabsets, the whole thing is a no-op?

[josevalim]

💚 💙 💜 💛 ❤️

[liamcmitchell]

Fantastic. Btw, I assume if there are no tabsets, the whole thing is a no-op?

Exactly!