SearchBar's clearIcon to have ability to always stay visible

**Is your feature request related to a problem? Please describe.**
The simple task of always showing the clearIcon even when no text is input.

**Describe the solution you'd like**
An "alwaysShowClearIcon" boolean prop on the SearchBar component.

**Describe alternatives you've considered**
Using the "right" prop and custom "icon" props.

从 SearchBar 组件开始，检查输入为空时如何确定 clearIcon 的可见性。添加所请求的 alwaysShowClearIcon 选项，并验证没有文本时清除图标仍保持可见，同时在不使用该选项时保留现有行为。

由索引模型根据 Issue 内容生成。