add Wire::end() for busio

[hathach]

• Mostly to add Wire:end() for busio https://github.com/adafruit/Adafruit_BusIO/pull/68
• all new code is cherry-picked from upstream Wire (without the timeout hanlding since it has potential to break existing code) https://github.com/arduino/ArduinoCore-avr/tree/master/libraries/Wire/src and should have no changes in existing code
• Some format/index to match upstream, make it easier to sync later on should we need to