WiP: Add DTO codegen

[manosbatsis]

Nice work! Thought best to try contributing for my personal needs VS forking. This WiP PR adds support for generating DTOs, i.e. #9 nullable mutables that can be used for partial updates, e.g.

@FactoryFunctionImpl(Visibility.INTERNAL)
@ImmutableImpl(Visibility.INTERNAL)
@DtoImpl(Visibility.INTERNAL)
@MutableImpl(Visibility.INTERNAL)
@BuilderImpl(visibility = Visibility.INTERNAL)
@DSLBuilderImpl("sampleDSL", type = DSLBuilderImpl.Type.WITH_ACCESSORS, visibility = Visibility.INTERNAL)
interface Sample {
    val sample: String
    val number: Int
}

Will generate:

internal class DtoSample(
  public var sample: String?,
  public var number: Int?
) : Dto<Sample>

internal fun Sample.toDto(): DtoSample = DtoSample(sample, number)

internal fun Sample.toPatched(patch: Sample): Sample {
  val isMutable = this is MutableSample
  val base = if(isMutable) this as MutableSample else this.toMutable()
  patch.sample?.let{ 
    base.sample = it
  }
  patch.number?.let{ 
    base.number = it
  }
  return if(isMutable) this else base.toImmutable()
}

The toPatched shouldn't be so dependent on the generated MutableSample of course, see #11

[y9vad9]

older version?

[y9vad9]

I think we should check type nullability