Generate all bodies in interfaces as default methods

compiler/testData/codegen/java8/box/jvm8/simpleProperty.kt

@@ -0,0 +1,13 @@
+// JVM_TARGET: 1.8
+
+interface Z {
+    val z: String;
+        get() = "OK"
+}
+
+
+class Test : Z
+
+fun box() : String {
+    return Test().z
+}