AutoComplete 的 customItem 属性缺少定义

[frankLife]

Description

未定义属性，无法在 ts 中使用

Reproduce Steps

https://github.com/ElemeFE/element-react/blob/master/typings/index.d.ts#L806

Solution

求添加

[frankLife]

@sam019

[frankLife]

在子元素中使用的 scrollbar 组件中的 resize 处理怀疑有问题，多次输入选择后会很卡顿

[fhaze]

AutoComplete component performance is very compromised by this scrollbar resize-event. Every time you filter something it becomes slower.