disposeMercuryIsolate function
Implementation
void disposeMercuryIsolate(int contextId) {
Pointer<Void> mercuryIsolate = _allocatedMercuryIsolates[contextId]!;
_disposeMercuryIsolate(dartContext.pointer, mercuryIsolate);
_allocatedMercuryIsolates.remove(contextId);
}