Fixed Serialization Issue #9

[chRyNaN]

This PR fixes Issue #9

Changes

• Exposed the kotlinx.serialization and com.chrynan.parcelable dependencies so that users of the library will not have to manually include those dependencies as they are now transitive
• Fixed incorrect use of the default Parcelable object instead of the parcelable parameter value in the rememberSavableNavigator functions
• Manually implemented a KSerializer for Navigator
• Manually implemented serializers for NavigationEvent s and NavigationEvent.Forward sealed classes

Issue Description

Issue #9 was occurring because of the way kotlinx.serialization handles sealed class polymorphic serialization with generic types. The generated serializer for sealed classes with generic types, apparently requires manually registering every type that will be used with that class. This is not very flexible, so to fix this, I created a NavigationEvent.Snapshot class that was not serializable and contained all the values every NavigationEvent could have. Then I implemented custom serializers for NavigationEvent and its subclass NavigationEvent.Forward (which too is a sealed class) and delegated to the NavigationEvent.Snapshot generated serializer, converting that to and from the appropriate types. This seemed to solve the issue.