[Test] Properly merge box against java testdata into codegen/box

Previous commit about it was 3199ce03 and it was completely wrong

compiler/testData/codegen/box/sam/samConstructorGenericSignature.kt

@@ -0,0 +1,28 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// DONT_TARGET_EXACT_BACKEND: JS JS_IR JS_IR_ES6 WASM NATIVE
+// SKIP_JDK6
+// WITH_RUNTIME
+// MODULE: lib
+// FILE: JavaClass.java
+
+class JavaClass {
+    interface Computable<T> {
+        T compute();
+    }
+
+    static <T> T compute(Computable<T> computable) {
+        return computable.compute();
+    }
+}
+
+// MODULE: main(lib)
+// FILE: 1.kt
+
+import java.util.Arrays
+
+fun box(): String {
+    val r: JavaClass.Computable<String> = JavaClass.Computable { "OK" }
+    val supertypes = Arrays.toString(r.javaClass.getGenericInterfaces())
+    if (supertypes != "[JavaClass\$Computable<java.lang.String>]") return "Fail: $supertypes"
+    return JavaClass.compute(r)!!
+}