Add tests for compilation against abi classes

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

@@ -0,0 +1,10 @@
+package app
+
+import lib.*
+
+fun runAppAndReturnOk(): String {
+    val a = A.create(10)
+    if (a.x != 20) error("a.x is '${a.x}', but is expected to be '20'")
+
+    return "OK"
+}

plugins/jvm-abi-gen/testData/compile/privateOnlyConstructors/lib/classes.kt

@@ -0,0 +1,7 @@
+package lib
+
+class A private constructor(val x: Int) {
+    companion object {
+        fun create(x: Int): A = A(x * 2)
+    }
+}