useComputed 似乎和 withHooks 并非强相关？

[luan]

useComputed 中会先判断 ensureCurrentInstance，而后者的提示是 “can only be called in a function passed to withHooks”；但核心逻辑只是判断 currentInstance，用 hooks mixin 的方法也能确保，提示似乎不妥