HartdwareSerial: recover original Arduino asynchronous write API#1503

fpistm merged 4 commits intostm32duino:masterstm32duino/Arduino_Core_STM32:masterfrom

ABOSTM:HARDWARESERIAL_ASYNCHRONOUS_APIABOSTM/Arduino_Core_STM32:HARDWARESERIAL_ASYNCHRONOUS_APICopy head branch name to clipboard