* Adding GpioPin

* adjusting based on PR feedback

* Adjusting to have natively drivers.

* make methods virtual

* adding Toggle to System.Device drivers

* Board and Mcp23xxx adjustments

* adding FT4222, FT232H and Pcx857x

* adding Arduino and Seasaw

* adjsting file encoding after conflict merge

* Adding missing Toggle implementation in Arduino native

* Adjusting test for new pattern with GpioPin

* adjusting PR feedback

* typo in test

* fixing nit

* fixing test

* fixing test

This "compiler" (actually a metadata converter and code analyzer) can take a compiled Iot program written using the Arduino binding and flash it as a standalone application to an ESP32 or similar 32-bit microcontroller.

Test and debug your application on the PC using the Arduino binding, and when everything works as expected, just flash it to the ESP32 and run it without the PC.

There are still a lot of open ends, but several more-or-less complex programs already work (see the WeatherStation example). Further documentation (both on usage as well as on internals) is still to be written.

See Readme for further instructions.

* Add possibility to set the alternate pin mode on Raspberry Pis

This is a split from PR #1128

* A few members renamed

* Changed according discussion

* Board class concept, with implementation for existing boards

Handles pin management and special pin modes.
Is one interface (as well as typically one instance) to keep everything together.

* Extra GPIO drivers, used for testing

DummyGpioDriver is a driver that has no pins, but can be
instantiated regardless of any hardware support.

KeyboardGpioDriver is a driver that uses the keyboard as GPIO "pins".

* Separate tests for hardware and software CS for SPI.

* Update src/devices/Board/Board.cs
Co-authored-by: NKrzysztof Wicher <mordotymoja@gmail.com>

* Change AlternatePinMode to class, so that it is extensible

* Remove pinAssignment capability from GpioController for now

Might be interfering with the proposed IGpioPin approach

* Fix unit tests

* That test was quite pointless. Now it fails (will fix later)

* Rebase on latest proposed low-level implementation

* Some nullability fixes

* Add documentation

* Add documentation

* Some missing headers, again

* Add AnalogOut as valid usage

* Replace I2cDeviceManager with I2cBus, per #1335

* Adjustments to new I2cBus class

* Add I2cBus scan function

* Fix comment

* Properly use the I2cBus

Make I2cBusManager a wrapper around it

* Fix unit test

* Logging will be provided in separate PR

* Minor review comments addressed

* Changed AlternatePinMode -> ExtendedPinMode, splitted up to base class and driver-specific implementation

* Missing core changes

* Adaptions to latest core interfaces

* Remove now duplicate change

* Add Board as base class of existing ArduinoBoard

* Fix unit test (Initialize is not public)

* Remove support for physical numbering scheme

Adds complexity to the API for a rarely used feature.

* Clean up usage in samples

* Clean up Board creation

* Minor cleanup

* Move implementation to base

* Remove unused functions
Co-authored-by: NKrzysztof Wicher <mordotymoja@gmail.com>