fix(ssr): make computed inactive during ssr, fix memory leak

fix #5208

packages/runtime-core/src/apiComputed.ts

@@ -0,0 +1,7 @@
+import { computed as _computed } from '@vue/reactivity'
+import { isInSSRComponentSetup } from './component'
+
+export const computed = ((getterOrOptions: any, debugOptions?: any) => {
+  // @ts-ignore
+  return _computed(getterOrOptions, debugOptions, isInSSRComponentSetup)
+}) as typeof _computed

packages/runtime-core/src/index.ts

@@ -3,7 +3,6 @@
 export const version = __VERSION__
 export {
   // core
-  computed,
   reactive,
   ref,
   readonly,
@@ -34,6 +33,7 @@ export {
   getCurrentScope,
   onScopeDispose
 } from '@vue/reactivity'
+export { computed } from './apiComputed'
 export {
   watch,
   watchEffect,