Add API for writable object property lists (#1206)

Added a new API for writable property lists across all the basic example object types, preparing for the introduction of a Writable_Property_List property in every object in a future BACnet standard revision.

The lists can be used by backup and restore feature to automatically choose the object property values in the backup that can be restored via internal WriteProperty directly from BACnet CreateObject services with  List of Initial Values. 

Updated existing device object examples to include these writable property lists.

src/bacnet/basic/object/channel.c

@@ -79,6 +79,20 @@ static const int32_t Channel_Properties_Optional[] = { -1 };
 
 static const int32_t Channel_Properties_Proprietary[] = { -1 };
 
+/* Every object shall have a Writable Property_List property
+   which is a BACnetARRAY of property identifiers,
+   one property identifier for each property within this object
+   that is always writable.  */
+static const int32_t Writable_Properties[] = {
+    /* unordered list of always writable properties */
+    PROP_PRESENT_VALUE,
+    PROP_OUT_OF_SERVICE,
+    PROP_LIST_OF_OBJECT_PROPERTY_REFERENCES,
+    PROP_CHANNEL_NUMBER,
+    PROP_CONTROL_GROUPS,
+    -1
+};
+
 /**
  * Returns the list of required, optional, and proprietary properties.
  * Used by ReadPropertyMultiple service.
@@ -108,6 +122,20 @@ void Channel_Property_Lists(
     return;
 }
 
+/**
+ * @brief Get the list of writable properties for a Channel object
+ * @param  object_instance - object-instance number of the object
+ * @param  properties - Pointer to the pointer of writable properties.
+ */
+void Channel_Writable_Property_List(
+    uint32_t object_instance, const int32_t **properties)
+{
+    (void)object_instance;
+    if (properties) {
+        *properties = Writable_Properties;
+    }
+}
+
 /**
  * @brief Get a Channel object
  * @param object_instance [in] BACnet object instance number