gtestutils: Add g_test_get_path() API

I found myself wanting to know the test that is currently being run,
where e.g. __func__ would be inconvenient to use, because e.g. the place
the string was needed was not in the test case function. Using __func__
also relies on the test function itself containing the whole path, while
loosing the "/" information that is part of the test path.

glib/gtestutils.h

@@ -338,6 +338,10 @@ void    g_test_add_data_func_full       (const char     *testpath,
                                          GTestDataFunc   test_func,
                                          GDestroyNotify  data_free_func);
 
+/* tell about currently run test */
+GLIB_AVAILABLE_IN_2_68
+const char * g_test_get_path            (void);
+
 /* tell about failure */
 GLIB_AVAILABLE_IN_2_30
 void    g_test_fail                     (void);