Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/reflection/properties/getPropertiesMutableVsReadonly.kt

@@ -0,0 +1,21 @@
+// WITH_REFLECT
+
+import kotlin.reflect.*
+
+class A(val readonly: String) {
+    var mutable: String = "before"
+}
+
+fun box(): String {
+    val props = A::class.java.kotlin.memberProperties
+    val readonly = props.single { it.name == "readonly" }
+    assert(readonly !is KMutableProperty1<A, *>) { "Fail 1: $readonly" }
+    val mutable = props.single { it.name == "mutable" }
+    assert(mutable is KMutableProperty1<A, *>) { "Fail 2: $mutable" }
+
+    val a = A("")
+    mutable as KMutableProperty1<A, String>
+    assert(mutable.get(a) == "before") { "Fail 3: ${mutable.get(a)}" }
+    mutable.set(a, "OK")
+    return mutable.get(a)
+}