Migrate boxWithJava tests to multi-file framework

compiler/testData/codegen/boxWithJava/secondaryConstructors/withVarargs.kt

@@ -0,0 +1,33 @@
+// FILE: WithVarargs.java
+
+public class WithVarargs {
+    public static String foo() {
+        return new A("1", "2", "3").getProp();
+    }
+}
+
+// FILE: withVarargs.kt
+
+fun join(x: Array<out String>): String {
+    var result = ""
+    for (i in x) {
+        result += i
+        result += "#"
+    }
+
+    return result
+}
+
+class A {
+    val prop: String
+    constructor(vararg x: String) {
+        prop = join(x)
+    }
+}
+
+fun box(): String {
+    val a1 = WithVarargs.foo()
+    if (a1 != "1#2#3#") return "fail1: ${a1}"
+
+    return "OK"
+}