[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/callableReference/publicMutableField.kt

@@ -0,0 +1,20 @@
+// DONT_TARGET_EXACT_BACKEND: JS JS_IR JS_IR_ES6 WASM NATIVE
+// MODULE: lib
+// FILE: A.java
+
+public class A {
+    public int field = 239;
+}
+
+// MODULE: main(lib)
+// FILE: 1.kt
+
+fun box(): String {
+    val a = A()
+    val f = A::field
+    if (f.get(a) != 239) return "Fail 1: ${f.get(a)}"
+    f.set(a, 42)
+    if (f.get(a) != 42) return "Fail 2: ${f.get(a)}"
+    if (f.get(a) != 42) return "Fail 2: ${f.get(a)}"
+    return "OK"
+}