Add multi-return for snow simulation

[PawelLiberadzki]

Description

This PR introduces two things (based on updates to RGL library):

• new implementation of LiDAR return modes - there are more return modes available and they are independent of laser beam divergence,
• update to snow simulation for multi-return feature - now snow simulation works correctly with updated return modes and divergence; what is also important, snow simulation, return modes and beam divergence are independent on each other, e.g. user may decide to turn on snow simulation, choose single return mode 'first', and turn off beam divergence - each setup should work correctly.