fix(runtime-core): avoid the proxy object polluting the slots of the internal instance (#3698)

fix #3695

packages/runtime-core/src/componentRenderContext.ts

@@ -89,7 +89,8 @@ export function withCtx(
   // mark this as a compiled slot function.
   // this is used in vnode.ts -> normalizeChildren() to set the slot
   // rendering flag.
-  renderFnWithContext._c = true
+  // also used to cache the normalized results to avoid repeated normalization
+  renderFnWithContext._c = renderFnWithContext
   if (__COMPAT__ && isNonScopedSlot) {
     renderFnWithContext._nonScoped = true
   }