Supported converting member properties to extensions

Additionally, we now generate <selection>throw UnsupportedOperationException()</selection> when a missing body is added

idea/testData/intentions/declarations/convertMemberToExtension/varWithGetter.kt.after

@@ -0,0 +1,10 @@
+class Owner {
+}
+
+var Owner.p: Int
+    get {
+        return 1
+    }
+    set(value) {
+        <caret><selection>throw UnsupportedOperationException()</selection>
+    }