jvm-abi-gen: Add tests for uses of private Kotlin classes from Java

plugins/jvm-abi-gen/testData/compile/privateClassesFromJavaApp/app/app.kt

@@ -0,0 +1,7 @@
+package app
+
+import lib.J
+
+fun runAppAndReturnOk(): String {
+    return J.result()
+}

plugins/jvm-abi-gen/testData/compile/privateClassesFromJavaApp/app/lib/J.java

@@ -0,0 +1,7 @@
+package lib;
+
+public class J {
+    public static String result() {
+        return new A().result();
+    }
+}

plugins/jvm-abi-gen/testData/compile/privateClassesFromJavaApp/lib/lib.kt

@@ -0,0 +1,5 @@
+package lib
+
+private class A {
+    fun result() = "OK"
+}