Compiler plugin breaks for data schemas with duplicate name

file1.kt:
```kt
@DataSchema
private interface A {
    // TODO
}

private fun DataFrame<A>.something() = TODO()
```

file2.kt:
```kt
@DataSchema
private interface A {
    val a: Int
}

private fun DataFrame<A>.something() {
    // some implementation
}
```

Especially common in a teaching scenario where one file is the exercise and the second once contains the solution.