feat: The <Affix> run update-position when first mounted, to get the actual styles.

components/affix/index.tsx

@@ -218,6 +218,8 @@ export default class Affix extends React.Component<AffixProps, AffixState> {
     // Wait for parent component ref has its value
     this.timeout = setTimeout(() => {
       this.setTargetEventListeners(target);
+      // Mock Event object.
+      this.updatePosition({} as Event);
     });
   }