Merge K2 box tests to main box tests

compiler/testData/codegen/box/properties/backingField/backingFieldVisibility.kt

@@ -0,0 +1,18 @@
+// TARGET_BACKEND: JVM_IR
+// IGNORE_BACKEND_K1: JVM_IR
+
+class A {
+    val a: Number
+        private field = 1
+
+    val b: Number
+        internal field = a + 3
+}
+
+fun box(): String {
+    return if (A().b + 20 == 24) {
+        "OK"
+    } else {
+        "fail: A().b = " + A().b.toString()
+    }
+}