Use the fully qualified class name instead of the simple class name in the serial name of polymorphic descriptors

[werner77]

Right now the serial name of a polymorphic descriptor is of the following form

kotlinx\.serialization\.(Polymorphic|Sealed)<(.*)>

Where the second capture group (part between angular brackets is the simple name of the base class. This can lead to a name clash when multiple base classes exist with the same simple name. For this reason it makes sense to use the fully qualified name instead.