建议添加全局 Loading icon 配置或单独 Loading icon 配置

[a81n9]

trafficstars

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

What problem does this feature solve?

使带有 loading 效果的组件支持自定义 loading 效果，比如 Button、异步对话框 等

What does the proposed API look like?

loading-icon (component | v-slot)