Initial Longer3D LK1/2 (Alfawise U20/U20+/U30) support (#14597)

.travis.yml

Marlin/src/core/boards.h

Marlin/src/module/temperature.cpp

Marlin/src/pins/pins.h

Marlin/src/pins/stm32/pins_LONGER3D_LK.h

Marlin/src/pins/stm32/pins_MKS_ROBIN.h

Marlin/src/pins/stm32/pins_MKS_ROBIN_MINI.h

Marlin/src/pins/stm32/pins_MKS_ROBIN_NANO.h

buildroot/share/PlatformIO/ldscripts/alfawise_Ux0.ld

buildroot/share/PlatformIO/scripts/alfawise_Ux0.py

buildroot/share/tests/alfawise_U20-tests

config/examples/Alfawise/U20/Configuration.h

config/examples/Alfawise/U20/Configuration_adv.h

config/examples/Alfawise/U20/_Statusscreen.h

platformio.ini