* `ledcWriteTone()` added a `apbcallback()` evertime the tone value was non zero.
* `addApbChangeCallback()` did not detect duplicate callbacks.
* changed the apbcallback list to a double link to support roll forward, roll back execution. This made the sequences of clock change callback start with the newest registered -> to oldest on the `before` then oldest -> newest after the clock change. This made the UART debug log output have minimal gibberish during the clock change.
* change how the UART callback handled the MUTEX because if any `apbchangeCallback()` executed a `log_x()` a deadlock would occur.
This fixes#3555
9ad860758c