Enable custom signal tones in LE mode.

This makes movement_play_signal synchronous when in LE mode, despite
using the underlying asynchronous API. It's a bit of a hack, but it
should work well enough for now.

This also moves the enabling/disabling of the buzzer into the
movement_play_signal function, so that watch faces no longer have to do
it.

watch-library/hardware/watch/watch_buzzer.c

@@ -90,6 +90,15 @@ void watch_buzzer_play_sequence(int8_t *note_sequence, void (*callback_on_end)(v
     _tc3_start();
 }
 
+uint16_t sequence_length(int8_t *sequence) {
+    uint16_t result = 0;
+    int i = 0;
+    while (sequence[i++]) {
+        result += sequence[i++];
+    }
+    return result;
+}
+
 void cb_watch_buzzer_seq(void) {
     // callback for reading the note sequence
     if (_tone_ticks == 0) {

watch-library/shared/watch/watch_buzzer.h

@@ -175,6 +175,8 @@ extern const uint16_t NotePeriods[108];
   */
 void watch_buzzer_play_sequence(int8_t *note_sequence, void (*callback_on_end)(void));
 
+uint16_t sequence_length(int8_t *sequence);
+
 /** @brief Aborts a playing sequence.
   */
 void watch_buzzer_abort_sequence(void);