OOM exception building really long routes

**Android API:any
**Mapbox Navigation SDK version:1.4.0

Steps to trigger behavior

1. Build long route (thousand of kimoleters)
2. App crashes randomly, depending on memory of the device.

Crash happens within DirectionsJsonObject at GSON serialization with the following stacktrace :

E/AndroidRuntime(11384): java.lang.OutOfMemoryError: Failed to allocate a 3690812 byte allocation with 2202366 free bytes and 2MB until OOM
E/AndroidRuntime(11384): 	at java.lang.String.<init>(String.java:400)
E/AndroidRuntime(11384): 	at java.lang.AbstractStringBuilder.toString(AbstractStringBuilder.java:633)
E/AndroidRuntime(11384): 	at java.lang.StringBuffer.toString(StringBuffer.java:723)
E/AndroidRuntime(11384): 	at java.io.StringWriter.toString(StringWriter.java:100)
E/AndroidRuntime(11384): 	at com.google.gson.Gson.toJson(Gson.java:639)
E/AndroidRuntime(11384): 	at com.google.gson.Gson.toJson(Gson.java:618)
E/AndroidRuntime(11384): 	at com.mapbox.api.directions.v5.models.DirectionsJsonObject.toJson(DirectionsJsonObject.java:30)
E/AndroidRuntime(11384): 	at com.mapbox.navigation.navigator.internal.MapboxNativeNavigatorImpl$setRoute$2.invokeSuspend(MapboxNativeNavigatorImpl.kt:150)
E/AndroidRuntime(11384): 	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
E/AndroidRuntime(11384): 	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
E/AndroidRuntime(11384): 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
E/AndroidRuntime(11384): 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
E/AndroidRuntime(11384): 	at java.lang.Thread.run(Thread.java:818)

From my analysis reason is that nav native implementation accepts route as a single string thus fails if string becomes really large.
While possible solutions are to pass some Json/Route object entity instead of string, temporary workaround returning some error instead of throwing an exception from background thread would also be nice.

cc @mapbox/navigation-android @mskurydin

Beginne mit services-directions-models/src/main/java/com/mapbox/api/directions/v5/models/DirectionsJsonObject.java und dessen toJson-Aufruf und verfolge dann MapboxNativeNavigatorImpl$setRoute$2 in Zeile 150. Reproduziere das Problem mit einer Route, die Tausende von Kilometern lang ist, und untersuche, wie die Route als einzelner String übergeben wird; die Änderung sollte den OutOfMemoryError im Hintergrundthread verhindern oder stattdessen einen Fehler zurückgeben.