ActivityIndicator upgrade

**Is your feature request related to a problem? Please describe.**
`ActivityIndicator is limited in customization and naming compared to modern UI needs.

**Describe the solution you'd like**
- Rename `ActivityIndicator` to `Spinner`
- Add more spinner variants

**Describe alternatives you've considered**
Using custom loaders or third-party spinner libraries.

**Additional context**
A Spinner component with multiple variants would improve flexibility and align better with Paper theme.

首先定位 react-native-paper 中现有的 ActivityIndicator 组件以及任何相关的测试或导出，然后查看项目中关于组件和主题的约定。在实现之前明确 Spinner API 和预期的变体；当组件完成重命名、支持多个变体，并且受影响的使用位置和测试都得到更新时，即视为完成。

由索引模型根据 Issue 内容生成。