Improve cloud shadow by using cloud buffer

[marpet]

The cloud buffer could be used to improve the cloud shadow.

This is already implemented but need validation. https://github.com/bcdev/snap-idepix/commit/0a97fe731fd3a729e57fbcd8dcaa7cc5db9cb782#diff-33e7af7c4b22273afd12f541388c1a98bdda20508b8375ffcd45320067dd4b06

[marpet]

This needs to be validated

[marpet]

• Actually, the link to the commit was something different.
• The usage of cloud buffer for the shadow calculation has been investigated, but it turned out that results were not better.