efficient way to do nextOff(long fromPosition) with Roaring64Bitmap

[nareshv]

Is your feature request related to a problem? Please describe.
Whats the recommended way to find nextOff(long fromPosition) to see whats the bit which is turned off from a given position ? This is useful to compress contiguous values

Describe the solution you'd like
When determining the contiguous ranges from the first value in the RoaringBitmap it is sometimes needed to find the next bit which is turned off. Any pointers on how this can be accomplished without getting the full entries, or using forEach() to traverse the bitmap and getting the desired value ?

Please note that this is a community-based project. Consider proposing a fix (code, documentation) as a pull request.