fix(runtime-core): ensure renderCache always exists

Author: yyx990803

packages/runtime-core/src/component.ts

@@ -114,7 +114,7 @@ export interface ComponentInternalInstance {
   accessCache: Data | null
   // cache for render function values that rely on _ctx but won't need updates
   // after initialized (e.g. inline handlers)
-  renderCache: (Function | VNode)[] | null
+  renderCache: (Function | VNode)[]
 
   // assets for fast resolution
   components: Record<string, Component>
@@ -192,7 +192,7 @@ export function createComponentInstance(
     effects: null,
     provides: parent ? parent.provides : Object.create(appContext.provides),
     accessCache: null!,
-    renderCache: null,
+    renderCache: [],
 
     // setup context properties
     renderContext: EMPTY_OBJ,

packages/runtime-core/src/componentProxy.ts

@@ -51,7 +51,6 @@ const publicPropertiesMap: Record<
 > = {
   $: i => i,
   $el: i => i.vnode.el,
-  $cache: i => i.renderCache || (i.renderCache = []),
   $data: i => i.data,
   $props: i => i.propsProxy,
   $attrs: i => i.attrs,