py/qstr: Add QSTR_TOTAL() macro to get number of qstrs.

py/qstr.h

@@ -56,6 +56,7 @@ typedef struct _qstr_pool_t {
 } qstr_pool_t;
 
 #define QSTR_FROM_STR_STATIC(s) (qstr_from_strn((s), strlen(s)))
+#define QSTR_TOTAL() (MP_STATE_VM(last_pool)->total_prev_len + MP_STATE_VM(last_pool)->len)
 
 void qstr_init(void);