[PROPOSAL] Support for MCUs with Built-in Temperature Sensor

[brentru]

Boards containing a MCU with a built-in temperature sensor (which measures the chip itself) do not have this sensor on a "pin" as it's within the silicon and accessed via an API call.

Proposing to add a flag to each board that contains silicon supporting this functionality. The flag would enable/show the MCU Temperature Sensor component in the picker.

Example for rpi-pico-w/definition.json

{
    "boardName":"rpi-pico-w",
    "mcuName":"rp2040",
    "mcuRefVoltage":3.3,
    "mcuHasTempSensor":true,
...

Relevant to adafruit/Adafruit_Wippersnapper_Arduino#390