libsysprof-capture: add sysprof_collector_log_printf()

This is a convenience function to call sysprof_collector_log() while also
formatting the message.

Ideally we'd be able to avoid the string format if we are not currently
collecting data, but that can be left for a future commit. We don't have
recursive locks so we need to duplicate the structure setup.

src/libsysprof-capture/sysprof-collector.c

@@ -454,3 +454,19 @@ sysprof_collector_log (GLogLevelFlags  severity,
 
   } COLLECTOR_END;
 }
+
+void
+sysprof_collector_log_printf (GLogLevelFlags  severity,
+                              const gchar    *domain,
+                              const gchar    *format,
+                              ...)
+{
+  g_autofree gchar *formatted = NULL;
+  va_list args;
+
+  va_start (args, format);
+  formatted = g_strdup_vprintf (format, args);
+  va_end (args);
+
+  sysprof_collector_log (severity, domain, formatted);
+}