Merge K2 box tests to main box tests

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

@@ -0,0 +1,19 @@
+// TARGET_BACKEND: JVM_IR
+// IGNORE_BACKEND_K1: JVM_IR
+
+var that: Int
+    lateinit field: String
+    get() = field.length
+    set(value) {
+        field = value.toString()
+    }
+
+fun box(): String {
+    that = 1
+
+    return if (that == 1) {
+        "OK"
+    } else {
+        "fail: $that"
+    }
+}