Unresolved reference for nested message used in other top-level message

[andrewparmet]

This is valid protobuf but protokt's generated code fails to compile:

message Foo {
  message Bar {}
}

message Baz {
  Foo.Bar bar = 1;
}

class Baz
private constructor(
    val bar: Bar?,
    val unknownFields: UnknownFieldSet = UnknownFieldSet.empty()
) : KtMessage {

needs to become:

class Baz
private constructor(
    val bar: Foo.Bar?,
    val unknownFields: UnknownFieldSet = UnknownFieldSet.empty()
) : KtMessage {