feat: new watchSyncEffect api

Author: antfu

src/apis/watch.ts

@@ -400,6 +400,10 @@ export function watchPostEffect(effect: WatchEffect) {
   return watchEffect(effect, { flush: 'post' })
 }
 
+export function watchSyncEffect(effect: WatchEffect) {
+  return watchEffect(effect, { flush: 'sync' })
+}
+
 // overload #1: array of multiple sources + cb
 // Readonly constraint helps the callback to correctly infer value types based
 // on position in the source array. Otherwise the values will get a union type