Release v1.2.0

Rebuild from more recent Mbed CE, add initial Arduino Giga and Portenta support

To use these compiled cores, extract them into a subfolder of the the hardware folder in your Arduino sketchbook. For example, on my Windows machine, I have:

C:\Users\jamie\Documents\Arduino\hardware\mbed-ce\ArduinoCore-mbed-ce-ARDUINO_NICLA_SENSE_ME-Release-1.1.0

and this folder contains boards.txt, platform.txt, etc.

After extracting the core to this folder, you should be able to select it from the menu in Arduino IDE:

Each core comes in 2 variants: Debug and Release. The Release core is small, but does not allow debugging. The Debug core is compiled with debug symbols, so you can use it with the IDE's debugger and debug your code.