ios 环境下使用input时用中文输入法，在输入拼音时会持续触发input事件

背景是需要做一个具有联想的搜索框，所以想用input事件没输入一个字就发送一次搜索请求

## Describe the bug
在ios下使用自带的键盘，假如输入‘我’字，拼音‘w o',输入完成后会出发三次：‘w’,'wo','我'，希望提供一个方法只有在输入完成后才触发或者能知道键盘的输入状态

## To Reproduce

## Environment
* Device: iPhone13
* OS:iOS15.4.0
* Version0.18.0

## Expected behavior
希望提供一个方法只有在输入完成后才触发或者能知道键盘的输入状态

Start by reproducing the input behavior on an iPhone 13 running iOS 15.4 with Weex 0.18.0, then locate the input-event handling path. Done means defining and exposing a reliable way to distinguish intermediate pinyin composition from completed Chinese input, with behavior verified for the reported sequence.

Written by the indexing model from the issue text.