Migrate Snackbar snippets (showing and action)

[hamen]

Code snippets are for:

• https://developer.android.com/develop/ui/views/notifications/snackbar/showing
• https://developer.android.com/develop/ui/views/notifications/snackbar/action

List of modifications:

• Showing page: Added Kotlin snippets for creating and displaying a Snackbar using Snackbar.make() and .show(), as well as chained invocation (views module).
• Action page: Added Kotlin snippets for Snackbar.setAction with custom OnClickListener and SnackbarHost with SnackbarHostState in Compose (views and compose:snippets modules).

Snippets not migrated:

• Showing page lines 55-73: View-based CoordinatorLayout XML layout skeleton with legacy Support Library references.