[Test] Move KotlinAgainstKotlin tests under BlackBoxCodegen tests

compiler/testData/codegen/box/compileKotlinAgainstKotlin/kt21775.kt

@@ -0,0 +1,44 @@
+// MODULE: lib
+// FILE: lib.kt
+
+package lib
+
+class TestObserver<T> {
+    fun assertValue(valuePredicate: (T) -> Boolean): Unit = TODO()
+}
+
+class Single<T> {
+    fun test(): TestObserver<T> = TODO()
+}
+
+class Employee
+
+class Either<T>
+
+typealias DomainEither<T> = Either<T>
+typealias DomainSingle<T> = Single<DomainEither<T>>
+
+fun provideDomainSingle(): DomainSingle<Employee> = TODO()
+
+class CreateEmployeeUseCaseAccessor {
+    fun testNormalName() {
+        val testObs = provideDomainSingle().test()
+        testObs.assertValue { true }
+    }
+}
+
+// MODULE: main(lib)
+// FILE: main.kt
+
+import lib.*
+
+class CreateEmployeeUseCaseTest {
+    fun testNormalName() {
+        val testObs = provideDomainSingle().test()
+        testObs.assertValue { true }
+    }
+}
+
+fun box(): String {
+    return "OK"
+}