Migrate boxWithJava tests to multi-file framework

compiler/testData/codegen/boxWithJava/invokeOnSyntheticProperty.kt

@@ -0,0 +1,17 @@
+// FILE: JavaClass.java
+
+public class JavaClass {
+    public String getO() {
+        return "O";
+    }
+}
+
+// FILE: main.kt
+
+//  KT-9522 Allow invoke convention for synthetic property
+
+operator fun String.invoke() = this + "K"
+
+fun box(): String {
+    return JavaClass().o();
+}