S3mini support, and avoiding dangerous pins on -C3/-S2

[softhack007]

platformio.ini: new buildenv for esp32-S3 Mini/Zero with 4MB flash and 2MB PSRAM

AppModLeds: FastLED pins for -S3

AppModFixtureGen: change default LED pin 16 --> 2 (safe choice on all boards)

SysModPins:

• some improvements by using macros from arduino framework: NUM_DIGITAL_PINS and digitalPinIsValid()
• disable dangerous direct pin access on -S2-/-C3/-S3