Migrate boxWithJava tests to multi-file framework

compiler/testData/codegen/boxWithJava/classCompanion.kt

@@ -0,0 +1,32 @@
+// FILE: CompanionInitialization.java
+
+public class CompanionInitialization {
+
+    public static Object getCompanion() {
+        return ConcreteWithStatic.Companion;
+    }
+
+}
+
+// FILE: CompanionInitialization.kt
+
+interface IStatic
+
+open class Static(x: IStatic) {
+    fun doSth() {
+    }
+}
+
+class ConcreteWithStatic : IStatic {
+    companion object : Static(ConcreteWithStatic())
+}
+
+fun box(): String {
+    ConcreteWithStatic.doSth()
+
+    val companion: Any? = CompanionInitialization.getCompanion()
+    if (companion == null) return "fail 1"
+    if (companion != ConcreteWithStatic) return "fail 2"
+
+    return "OK"
+}