Reduce API indirection

[sargunv]

Just about every API we expose in maplibre-compose goes through multiple layers of indirection to the actual implementation:

• The KMP API, typically a pure Kotlin class or an expect/actual class
• Calls the platform API (MapLibre Android, MapLibre iOS, maplibre-native-bindings, etc)
• Calls the C++ native core API

Except for JS, where the KMP API calls the JS API.

Previously, the KMP API was the only one we controlled, and it's the one we used to unify the varying platform APIs. But with the native core integration for desktop, we now control one of the platform APIs, so we're now writing two layers ourselves instead of one.

Probably after #572, we should look at collapsing two of the layers into one, eliminating indirection and simplifying the API by matching the original one more closely.

The remaining complication will be in how to unify the native core and JS APIs into one.