Generate warnings if Pico STDIO init called

[earlephilhower]

Warn the user that the Pico SDK STDIO calls (stdio_init_all, stdio_usb_init, stdio_uart_init) are not supported or needed at compile time. See multiple issues #1433 #1347 #1273 #1251 and others.

[earlephilhower]

Users will get a nice explanatory message and links if they try to call unsupported pico-stdio calls:

In file included from /tmp/arduino_build_841677/sketch/sketch_may23a.ino.cpp:1:
/home/earle/Arduino/sketch_may23a/sketch_may23a.ino: In function 'void setup()':
/home/earle/Arduino/hardware/pico/rp2040/cores/rp2040/Arduino.h:138:44: error: static assertion failed: stdio_init_all is not supported or needed. Either use Serial.printf() or set the debug port in the IDE to Serial/1/2 and use printf().  See https://github.com/earlephilhower/arduino-pico/issues/1433#issuecomment-1540354673 and https://github.com/earlephilhower/arduino-pico/issues/1433#issuecomment-1546783109
  138 | #define stdio_init_all(...)  static_assert(0, "stdio_init_all is not supported or needed. Either use Serial.printf() or set the debug port in the IDE to Serial/1/2 and use printf().  See https://github.com/earlephilhower/arduino-pico/issues/1433#issuecomment-1540354673 and https://github.com/earlephilhower/arduino-pico/issues/1433#issuecomment-1546783109")
      |                                            ^
/home/earle/Arduino/sketch_may23a/sketch_may23a.ino:4:3: note: in expansion of macro 'stdio_init_all'
    4 |   stdio_init_all();
      |   ^~~~~~~~~~~~~~
exit status 1
Error compiling for board Raspberry Pi Pico.