Refactor: Improve ButtonGroup examples and opt-in to Material3 APIs

This commit refactors the ButtonGroup examples and related files. It also opts in to `ExperimentalMaterial3ExpressiveApi` and `ExperimentalMaterial3Api` in the `build.gradle.kts` file.

Key changes:
- Deleted `AppBarRowExample.kt` as it is no longer used.
- Renamed `ButtonGroupExample.kt` to `ButtonGroupComposable.kt` and updated its content.
- Updated `ButtonGroupListingScreen.kt` to include navigation to different ButtonGroup examples and improve the UI.
- Added `ConnectedButtonGroupComposable.kt` to showcase an example of a connected button group.
- Added "composables" to the project dictionary.
- Enabled `ExperimentalMaterial3ExpressiveApi` and `ExperimentalMaterial3Api` project-wide by adding compiler arguments in `app/build.gradle.kts`.