…bitbanged SPI mode for board using ArduinoCore-API

When using bit banged SPI, which the sketch did when compiled for any architecture other than AVR, a `SPISettings` class was declared by the sketch. At the time the sketch was written, it was reasonable to expect this would not cause a name collision, since SPI.h is not `#include`d when doing bit banged SPI. However, since then a `SPISettings` class has been declared in [ArduinoCore-API's HardwareSPI.h](https://github.com/arduino/ArduinoCore-API/blob/932c7c7d4d4d334b10484284cc846672ad59607c/api/HardwareSPI.h#L37), causing the ArduinoISP sketch to not compile for any board whose core uses ArduinoCoreAPI (currently Arduino Mega AVR Boards, "Arduino nRF528x Boards (Mbed OS]", and "Arduino Mbed OS Boards (nRF52840 / STM32H747)"):

```
  /github/workspace/examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino:191:27: error: reference to 'SPISettings' is ambiguous
       void beginTransaction(SPISettings settings) {
                             ^~~~~~~~~~~
  /github/workspace/examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino:167:7: note: candidates are: class SPISettings
   class SPISettings {
         ^~~~~~~~~~~
  In file included from /github/home/.arduino15/packages/arduino/hardware/megaavr/1.8.6/cores/arduino/api/ArduinoAPI.h:31:0,
                   from /github/home/.arduino15/packages/arduino/hardware/megaavr/1.8.6/cores/arduino/Arduino.h:23,
                   from /github/workspace/examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino:39:
  /github/home/.arduino15/packages/arduino/hardware/megaavr/1.8.6/cores/arduino/api/HardwareSPI.h:37:7: note:                 class arduino::SPISettings
   class SPISettings {
         ^~~~~~~~~~~
```

The fix is to use the `ARDUINO_API_VERSION` macro defined by ArduinoCore-API to detect when it is in use and make the bitbanged SPI code use the `SPISettings` class from ArduinoCore-API in this case.

…d OS

The name collision between the variable named "error" in the ArduinoISP sketch and a function of that name declared by Mbed OS causes compilation of the sketch to fail for boards that use the "Arduino nRF528x Boards (Mbed OS)" or "Arduino Mbed OS Boards (nRF52840 / STM32H747)" cores.