Add ESP32 WiFi interface (#11209)

.travis.yml

Marlin/Configuration_adv.h

Marlin/src/HAL/HAL_ESP32/HAL.cpp

Marlin/src/HAL/HAL_ESP32/HAL.h

Marlin/src/HAL/HAL_ESP32/WebSocketSerial.cpp

Marlin/src/HAL/HAL_ESP32/WebSocketSerial.h

Marlin/src/HAL/HAL_ESP32/ota.cpp

Marlin/src/HAL/HAL_ESP32/web.cpp

Marlin/src/HAL/HAL_ESP32/web.h

Marlin/src/HAL/HAL_ESP32/wifi.cpp

Marlin/src/HAL/HAL_ESP32/wifi.h

Marlin/src/HAL/HAL_LINUX/hardware/LinearAxis.cpp

Marlin/src/core/serial.h

Marlin/src/inc/SanityCheck.h

buildroot/share/tests/esp32-tests

config/default/Configuration_adv.h

config/examples/3DFabXYZ/Migbot/Configuration_adv.h

config/examples/AlephObjects/TAZ4/Configuration_adv.h

config/examples/AliExpress/UM2pExt/Configuration_adv.h

config/examples/Anet/A2/Configuration_adv.h