Convert GenericType or ResolvedType to JavaType

Some function like `Jackson2JsonRedisSerializer` requires `JavaType` as parameter. When I tried to pass generic type parameter via `GenericType` object, I find that `GenericType` can only be converted to `ResolvedType`, and there is no way from ResolvedType to JavaType.

```java
TypeResolver resolver = new TypeResolver();
GenericType gtype = new GenericType(){}
ResolvedType rtype = resolver.resolve(gtype);
// seems correct but constructType will throw when receiving GenericType!
JavaType javatype= TypeFactory.defaultInstance().constructType(rtype);
```