Consistency + alignment pass between iOS and Android Platform Public APIs

Before 1.0, we should take a second pass through all of the public APIs for iOS and Android to ensure they are aligned.

- The biggest area is related to observability and state models, so that's probably the first thing to do. See #780.
- Revisit the location subscription / provider model
- Speech (spoken instruction observers)
- Route providers

Start by reviewing issue #780 and comparing the public iOS and Android API surfaces, beginning with observability and state models. Then examine the location subscription/provider model, spoken instruction observers, and route providers; done means the listed public APIs are consistently aligned across both platforms.

Written by the indexing model from the issue text.