create a decorator for functions that remove and then expand auxiliary variables

[luitjansl]

there are several functions (currently in the package class) that call remove_expanded_auxiliary_variables_from_dataset before beginning their "work", and when they are finished they call expand_transient_auxiliary_variables(self).
Examples include the function "mask" and the function "regrid_like"

We could create a decorator to deal with the removing and expanding of auxiliary variables.

Based on a review comment in PR #907