Function splitId

splitId(id: string): NamespacedId | undefined
Split a composite id on its first :. Everything after it belongs to the provider.
Parameters
- id: string
  A composite id produced by namespaceId.
Returns NamespacedId | undefined
The two halves, or undefined when id has no provider prefix.
Example
```
splitId('private:direct:ab,cd'); // { providerId: 'private', innerId: 'direct:ab,cd' }
splitId('orphan'); // undefined
```