[perf] Improve string encoding performance by ~50%

Entity encoding is a large portion of time spent, since we encode all attribute values and text nodes.
This switches encoding from multiple regular expressions to a linear forward scan.

Author: developit

src/util.js

@@ -3,16 +3,25 @@ export const IS_NON_DIMENSIONAL = /acit|ex(?:s|g|n|p|$)|rph|grid|ows|mnc|ntw|ine
 
 const ENCODED_ENTITIES = /[&<>"]/;
 
-export function encodeEntities(input) {
-	const s = String(input);
-	if (!ENCODED_ENTITIES.test(s)) {
-		return s;
+export function encodeEntities(str) {
+	if (ENCODED_ENTITIES.test(s) === false) return s;
+	let start = 0,
+		i = 0,
+		out = '',
+		ch = '';
+	for (; i<str.length; i++) {
+		switch(str.charCodeAt(i)) {
+			case 60: ch = '&lt;'; break;
+			case 62: ch = '&gt;'; break;
+			case 34: ch = '&quot;'; break;
+			case 38: ch = '&amp;'; break;
+			default: continue;
+		}
+		if (i > start) out += str.slice(start, i);
+		out += ch;
+		start = i + 1;
 	}
-	return s
-		.replace(/&/g, '&amp;')
-		.replace(/</g, '&lt;')
-		.replace(/>/g, '&gt;')
-		.replace(/"/g, '&quot;');
+	return out + str.slice(start, i);
 }
 
 export let indent = (s, char) =>