feat: implement the loading indicator component

- The goal is to implement a loading indicator. This component is similar but not the same as progress indicators. The modern expressive version uses a set of shapes and morphing between them.
- Reuse the shapes added in https://github.com/callstack/react-native-paper/issues/4984
- See https://m3.material.io/components/loading-indicator/specs
- Reuse newly introduced tokens (shape, motion, typography, color etc)
- Extract component specific tokens for easier maintenance.
- Get inspired from TextInput/TextField, Switch, Checkbox, FAB components which have gone through modernization.
- Showcase the component in the example app
- Update the documentation

首先检查 issue #4984 中的 shapes 以及 Material 3 的 loading-indicator 规范。比较 TextInput/TextField、Switch、Checkbox 和 FAB 中的现代化模式，然后定义 component tokens 和实现范围。当 indicator 可在示例应用中使用且其文档已更新时，即表示完成。

由索引模型根据 Issue 内容生成。