[comp:select] 下拉框新增loading 效果

[danranVm]

• I have searched the issues of this repository and believe that this is not a duplicate.

What problem does this feature solve?

下拉框的数据源来自后端且数据量大，需要进行分页处理；希望动态修改 dataSource 的过程中有加载中的效果。

What does the proposed API look like?

<IxSelect :loading="loading" />

[idux-bot]

Translation of this issue:

[Comp: SELECT] drop -down box new Loading effect

• [] I have searched the [isSues] (https://github.com/iduxfe/idux/issues) of this repository and believe that this is not a duplicate.

What proplem does this feature solver?

The data source of the drop -down box comes from the back end and the data volume is large, which needs to be paged; I hope that there is a loading effect in the process of dynamic modification of DataSource.

What does the proposed api look like?

Ixselect: loading = "loading" />