Allow targeting multiple scopes in a single file with `targetScope`

Implementation for the syntax discussed e.g.
```bicep
targetScope = [
'tenant'
'subscription'
]
```

No source file, test, or entry point is named; start by reviewing the issue's proposed targetScope syntax and locating the language components that validate deployment scope. Done would require an agreed implementation for multiple scopes, including validation and coverage for the tenant and subscription examples.

Written by the indexing model from the issue text.