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

Start by reviewing the shapes from issue #4984 and the Material 3 loading-indicator specifications. Compare the modernization patterns in TextInput/TextField, Switch, Checkbox, and FAB, then define the component tokens and implementation scope. Done means the indicator is available in the example app and its documentation is updated.

Written by the indexing model from the issue text.