feat: v-once

Note: only compiler transform is tested - integration with runtime
still needs to be tested.

packages/runtime-core/src/createRenderer.ts

@@ -177,10 +177,15 @@ export function createRenderer<
     optimized: boolean = false
   ) {
     // patching & not same type, unmount old tree
-    if (n1 != null && !isSameType(n1, n2)) {
-      anchor = getNextHostNode(n1)
-      unmount(n1, parentComponent, parentSuspense, true)
-      n1 = null
+    if (n1 != null) {
+      if (!isSameType(n1, n2)) {
+        anchor = getNextHostNode(n1)
+        unmount(n1, parentComponent, parentSuspense, true)
+        n1 = null
+      } else if (n1.props && n1.props.$once) {
+        console.log(111)
+        return
+      }
     }
 
     const { type, shapeFlag } = n2