feat(runtime-core): 添加预冲洗回调队列功能

- 在 runtime-core 中新增 queuePreFlushCb 函数用于管理预冲洗回调
- 在 vue 包中导出 queuePreFlushCb 函数供外部使用
- 实现调度器中的回调队列机制，包括队列管理和执行逻辑
- 添加去重逻辑确保回调函数只执行一次
- 新增示例文件展示调度器预冲洗回调的使用方法

packages/runtime-core/src/index.ts

@@ -0,0 +1 @@
+export { queuePreFlushCb } from './scheduler'

packages/runtime-core/src/scheduler.ts

@@ -1 +1,35 @@
 let isFlushPending = false
+
+const resolvedPromise = Promise.resolve() as Promise<any>
+
+let currentFlushPromise: Promise<void> | null = null
+
+const pendingPreFlushCbs: Function[] = []
+export function queuePreFlushCb(cb: Function) {
+  queueCb(cb, pendingPreFlushCbs)
+}
+function queueCb(cb: Function, pendingQueue: Function[]) {
+  pendingQueue.push(cb)
+  queueFlush()
+}
+
+function queueFlush() {
+  if (!isFlushPending) {
+    isFlushPending = true
+    currentFlushPromise = resolvedPromise.then(flushJobs)
+  }
+}
+function flushJobs() {
+  isFlushPending = false
+  flushPreFlushCbs()
+}
+export function flushPreFlushCbs() {
+  if (pendingPreFlushCbs.length) {
+    //拷贝去重,类似深拷贝
+    let activePreFlushCbs = [...new Set(pendingPreFlushCbs)]
+    pendingPreFlushCbs.length = 0
+    for (let i = 0; i < activePreFlushCbs.length; i++) {
+      activePreFlushCbs[i]()
+    }
+  }
+}