Miscellaneous perf tweak (#10421)

* refactor: early return on hot path

* refactor: read next2 only when next is dot

* perf: mini refactor

packages/babel-parser/src/parser/comments.js

@@ -39,10 +39,11 @@ export default class CommentsParser extends BaseParser {
   }
 
   adjustCommentsAfterTrailingComma(node: Node, elements: Node[]) {
-    if (elements.length === 0) {
+    if (this.state.leadingComments.length === 0) {
       return;
     }
-    if (this.state.leadingComments.length === 0) {
+
+    if (elements.length === 0) {
       return;
     }