feat: implement Toolbar

- Implement the new component according to specs: https://m3.material.io/components/toolbars/overview
- 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 with the Material Design toolbar specification and compare the modernization work in TextInput/TextField, Switch, Checkbox, and FAB. Identify the component entry point, token definitions, example app area, and documentation location before changing anything. Done means the toolbar follows the specification, uses and exposes appropriate tokens, appears in the example app, and is documented.

索引モデルが issue の本文から書いたものです。