Add support for the onboard WiFi chip on the Raspberry Pi Pico W
(RP2040 based ) board using the arduino-pico Arduino core at
https://github.com/earlephilhower/arduino-pico
The PicoW WiFi stack is a mashup of the ESP8266 and ESP32 cores, so
only minimal changes were required. Defines a new NETWORK_TYPE for
the PicoW.
ESP8266 examples renames to ESP8266_PICO because they all work unmodified
(except for OTA which is handled differently on the Pico)
