feature: DefaultInputObjectMapper to support Kotlin non constructor fields

[bsamartins]

Describe the Feature Request

Currently, the DefaultInputObjectMapper only supports setting fields in Kotlin classes through constructor arguments. We have some use cases where we can't use the generated classes and need to build our own representation of the types with property delegates.

Describe Preferred Solution

The object mapper should support setting object properties.

class TestType(val name: String) {
  var email: String? = null
  ...
  var dob: LocalDate? by myDelegate
}

Describe Alternatives