add option to clip data to area of interest in l2 to l3 processing

[j-haacker]

Is your feature request related to a problem? Please describe.
For regions with scattered glaciers especially, I believe the performance could be increased by excluding data outside of glacierized areas, or in general, outside of the region of interest.

This was not implemented because excluding l2 point data can be costly for complex polygons. Maybe a pragmatic way would be to add an option to exclude points prior to processing. The complexity could maybe be reduce by using convex hulls, I believe.

Maybe there are even better ways?

Describe the solution you'd like
A better performing l2 to l3 algorithm.