Remove special support for FunctionalInterrupt from core interrupt handling:

- VIP treatment in general attach/detach/handling looks untidy:
  extern symbols without matching header include but copy&paste
  special under-the-hood c++ delete support, where everyone else has to do their own
  resource tracking as usual.
- FunctionalInterrupt is not used by anything inside core ESP8266 Arduino for 2 years now,
  it can be a library, which reduces precious core size for everyone else.

Expose attachInterruptArg via Arduino.h.

Author: dok-net

cores/esp8266/Arduino.h

@@ -217,6 +217,7 @@ void shiftOut(uint8_t dataPin, uint8_t clockPin, uint8_t bitOrder, uint8_t val);
 uint8_t shiftIn(uint8_t dataPin, uint8_t clockPin, uint8_t bitOrder);
 
 void attachInterrupt(uint8_t pin, void (*)(void), int mode);
+void attachInterruptArg(uint8_t pin, void (*)(void*), void * arg, int mode);
 void detachInterrupt(uint8_t pin);
 
 void preinit(void);