thread: implement some properties

Make helper method to parse thread properties and add 2 new properties
to control name and stack-size of the thread.
Use properties when creating threads with the default utils.
Use the default thread utils instead of pthread_create so that the
properties are used.

spa/include/spa/support/thread.h

@@ -135,6 +135,9 @@ static inline int spa_thread_utils_drop_rt(struct spa_thread_utils *o,
 	return res;
 }
 
+#define SPA_KEY_THREAD_NAME		"thread.name"		/* the thread name */
+#define SPA_KEY_THREAD_STACK_SIZE	"thread.stack-size"	/* the stack size of the thread */
+
 /**
  * \}
  */