add method
Add a marker to this collection.
The optional index parameter inserts the marker at a specific position; by
default the marker is appended to the end of the collection.
Parameters
marker: The Marker instance to add.index: Optional insert position. Use -1 to append (default).
Implementation
void add(final Marker marker, {final int index = -1}) {
objectMethod(pointerId, 'MarkerCollection', 'add', args: marker.pointerId);
}