Fix the regexp performance issue

Also move the addHoverClass implementation into the rebuild stage.
So if there is still some corner case we have not handled, it will
only affect the replayer part of rrweb.

src/snapshot.ts

@@ -17,36 +17,11 @@ export function resetId() {
   _id = 1;
 }
 
-const CSS_RULE = /(([#|\.]{0,1}[a-z0-9\[\]=:]+[\s|,]*)+)\s(\{[\s\S]?[^}]*})/;
-const CSS_RULE_GLOBAL = /(([#|\.]{0,1}[a-z0-9\[\]=:]+[\s|,]*)+)\s(\{[\s\S]?[^}]*})/g;
-const HOVER_SELECTOR = /([^\\]):hover/g;
-export function addHoverClass(cssText: string): string {
-  const matches = cssText.match(CSS_RULE_GLOBAL) || [];
-  for (const match of matches) {
-    const [, selectorText = '', , rules = ''] = match.match(CSS_RULE) || [];
-    const selectors = selectorText
-      .split(',')
-      .map(selector => selector.trim())
-      .map(selector => {
-        if (HOVER_SELECTOR.test(selector)) {
-          const newSelector = selector.replace(HOVER_SELECTOR, '$1.\\:hover');
-          selector += `, ${newSelector}`;
-        }
-        return selector;
-      });
-    cssText = cssText.replace(match, selectors.join(', ') + ' ' + rules);
-  }
-  return cssText;
-}
-
 function getCssRulesString(s: CSSStyleSheet): string | null {
   try {
     const rules = s.rules || s.cssRules;
     return rules
-      ? Array.from(rules).reduce(
-          (prev, cur) => (prev += addHoverClass(cur.cssText)),
-          '',
-        )
+      ? Array.from(rules).reduce((prev, cur) => (prev += cur.cssText), '')
       : null;
   } catch (error) {
     return null;
@@ -177,12 +152,10 @@ function serializeNode(n: Node, doc: Document): serializedNode | false {
       if (parentTagName === 'SCRIPT') {
         textContent = 'SCRIPT_PLACEHOLDER';
       }
-      if (parentTagName === 'STYLE') {
-        textContent = addHoverClass(textContent || '');
-      }
       return {
         type: NodeType.Text,
         textContent: textContent || '',
+        isStyle: parentTagName === 'STYLE' ? true : undefined,
       };
     case n.CDATA_SECTION_NODE:
       return {