Optimize js-obj for emitting object literals

[borkdude]

See https://github.com/clojure/clojurescript/blob/b7ede4bce3e273ab85155fdd8463c291a6f81d43/src/main/clojure/cljs/core.cljc#L2676C1-L2703C17

This will be a better way of emitting JS object literals than relying on metadata for users

Similarly array: https://github.com/clojure/clojurescript/blob/b7ede4bce3e273ab85155fdd8463c291a6f81d43/src/main/clojure/cljs/core.cljc#L2592