GVariant: add new g_variant_new_take_string() API

Lots of people have variously asked for APIs like
g_variant_new_string_printf() in order to avoid having to use
g_strdup_printf(), create a GVariant using g_variant_new_string(), then
free the temporary string.

Instead of supporting that, plus a million other potential cases,
introduce g_variant_new_take_string() as a compromise.

It's not possible to write:

 v = g_variant_new_take_string (g_strdup_printf (....));

to get the desired result and avoid the extra copies.  In addition, it
works with many other functions.

https://bugzilla.gnome.org/show_bug.cgi?id=698455

docs/reference/glib/glib-sections.txt

@@ -3108,6 +3108,7 @@ g_variant_new_uint64
 g_variant_new_handle
 g_variant_new_double
 g_variant_new_string
+g_variant_new_take_string
 g_variant_new_object_path
 g_variant_is_object_path
 g_variant_new_signature

glib/gvariant.c

@@ -1273,6 +1273,42 @@ g_variant_new_string (const gchar *string)
                                      string, strlen (string) + 1);
 }
 
+/**
+ * g_variant_new_take_string: (skip)
+ * @string: a normal utf8 nul-terminated string
+ *
+ * Creates a string #GVariant with the contents of @string.
+ *
+ * @string must be valid utf8.
+ *
+ * This function consumes @string.  g_free() will be called on @string
+ * when it is no longer required.
+ *
+ * You must not modify or access @string in any other way after passing
+ * it to this function.  It is even possible that @string is immediately
+ * freed.
+ *
+ * Returns: (transfer none): a floating reference to a new string
+ *   #GVariant instance
+ *
+ * Since: 2.38
+ **/
+GVariant *
+g_variant_new_take_string (gchar *string)
+{
+  GVariant *value;
+  GBytes *bytes;
+
+  g_return_val_if_fail (string != NULL, NULL);
+  g_return_val_if_fail (g_utf8_validate (string, -1, NULL), NULL);
+
+  bytes = g_bytes_new_take (string, strlen (string) + 1);
+  value = g_variant_new_from_bytes (G_VARIANT_TYPE_STRING, bytes, TRUE);
+  g_bytes_unref (bytes);
+
+  return value;
+}
+
 /**
  * g_variant_new_object_path:
  * @object_path: a normal C nul-terminated string

glib/gvariant.h

@@ -101,6 +101,8 @@ GLIB_AVAILABLE_IN_ALL
 GVariant *                      g_variant_new_double                    (gdouble               value);
 GLIB_AVAILABLE_IN_ALL
 GVariant *                      g_variant_new_string                    (const gchar          *string);
+GLIB_AVAILABLE_IN_2_38
+GVariant *                      g_variant_new_take_string               (gchar                *string);
 GLIB_AVAILABLE_IN_ALL
 GVariant *                      g_variant_new_object_path               (const gchar          *object_path);
 GLIB_AVAILABLE_IN_ALL