Move internal methods/variables out of sanitize closure.
Move internal methods/variables out of sanitize closure.

At the moment, they are re-evaluated on every call to DOMPurify#sanitize(),
which is unnecessarily work for subsequent calls.

ConradIrwin/DOMPurify,kwangkim/DOMPurify,voku/DOMPurify,togusafish/t-ashula-_-DOMPurify,tdeekens/DOMPurify,tdeekens/DOMPurify,voku/DOMPurify,Joris-van-der-Wel/DOMPurify,neilj/DOMPurify,kwangkim/DOMPurify,Joris-van-der-Wel/DOMPurify,tdeekens/DOMPurify,Joris-van-der-Wel/DOMPurify,neilj/DOMPurify,neilj/DOMPurify,togusafish/t-ashula-_-DOMPurify,ConradIrwin/DOMPurify