json-glib-1.0: Fix 'Json.Serializable' interface metadata

 - mark 'Serializable.find_property' nullable
 - mark 'Serializable.default_deserialize_property.value' as 'out'
   parameter

These should be fixed upstream with specific GIR annotations, but in the
meantime, it's important to have that interface usable.

Fix metadata indentation for, it was mixed with space and tabs.

https://bugzilla.gnome.org/show_bug.cgi?id=768380

Author: arteymix

vapi/json-glib-1.0.vapi

@@ -307,12 +307,12 @@ namespace Json {
 	[CCode (cheader_filename = "json-glib/json-glib.h,json-glib/json-gobject.h", type_id = "json_serializable_get_type ()")]
 	public interface Serializable : GLib.Object {
 		[Version (since = "0.10")]
-		public bool default_deserialize_property (string property_name, GLib.Value value, GLib.ParamSpec pspec, Json.Node property_node);
+		public bool default_deserialize_property (string property_name, out GLib.Value value, GLib.ParamSpec pspec, Json.Node property_node);
 		[Version (since = "0.10")]
 		public Json.Node default_serialize_property (string property_name, GLib.Value value, GLib.ParamSpec pspec);
 		public abstract bool deserialize_property (string property_name, out GLib.Value value, GLib.ParamSpec pspec, Json.Node property_node);
 		[Version (since = "0.14")]
-		public abstract unowned GLib.ParamSpec find_property (string name);
+		public abstract unowned GLib.ParamSpec? find_property (string name);
 		[Version (since = "0.14")]
 		public abstract GLib.Value get_property (GLib.ParamSpec pspec);
 		[CCode (array_length_pos = 0.1, array_length_type = "guint")]

vapi/metadata/Json-1.0.metadata

@@ -26,6 +26,8 @@ gvariant_deserialize_data unowned=false floating
 
 Object.add_member replacement="Json.Object.set_member"
 Serializable cheader_filename="json-glib/json-glib.h,json-glib/json-gobject.h"
-	     .deserialize_property.value out
+	.default_deserialize_property.value out
+	.deserialize_property.value out
+	.find_property nullable
 construct_gobject cheader_filename="json-glib/json-glib.h,json-glib/json-gobject.h" replacement="Json.gobject_from_data"
 serialize_gobject cheader_filename="json-glib/json-glib.h,json-glib/json-gobject.h" replacement="Json.gobject_to_data"