HardwareSerial::write(const char*, ...) API compatibility to AVR, ESP8266, et al

[dok-net]

The ESP32 Arduino implementation of HardwareSerial.h is missing

write(const char * buffer, size_t size);

Additionally, this PR adds the read(buffer, size) extension from ESP8266, also in EspSoftwareSerial, that complements the inherited Stream::readBytes() with a non-blocking variant.