Add support for external data classes or non-data classes

[brady-aiello]

If we have a data class we don't own, we should be able to deep print it somehow. Given:

data class SomeExternalClass(val name: String, val age: Int)

Not sure the best way to do this.

1. we might be able to generate SomeExternalClass.deepPrint() exactly once, and place it in a package that matches its declaration, if any instances are the properties of an annotated class, without any modification:

@DeepPrint
data class MyClass(val externalClass: SomeExternalClass)

2. or we give the processor a heads up about the class we need to generate it for:

@DeepPrint
data class MyClass(@DeepPrint val externalClass: SomeExternalClass)

3. or we can manually create a deep print function, and pass it as an optional parameter:

@DeepPrint
data class MyClass(@DeepPrint(with = ::myExternalClassDeepPrintFunction)val externalClass: SomeExternalClass)

fun myEternalClassDepPrintFunction(externalClass: SomeExternalClass) {
    println("""
        SomeExternalClass(
            val someProperty = ${externalClass.someProperty}
        )
    """).trimIndent()
}

Options 1 or 2 would be ideal, as it would require little to no extra work from the caller. The main issue with options 1 and 2 is getting enough information about the externally declared class. KSP is not being run on compiled code, and there is just less type information available. There might be a way to do this still, so it's worth taking another stab at.

Option 3 is probably the easiest to implement, and the most flexible. It would allow for any class from any module to be deep-printable. It does require an extra step. But, depending on the class in question, the benefit might outweigh the cost of writing another function.