Automatic partial resampling

With the current implementation of resampling, to get partial resampling, you can only do it by specifying it with the `dim_names` keyword argument. It may be helpful to assume that if the dimensions in `dest_var` is a strict subset of the dimensions in `src_var`, then the user want to resample over all the possible dimensions in `dest_var`.

Locate the current resampling implementation and the handling of the `dim_names` keyword, then inspect how dimensions in `src_var` and `dest_var` are compared. Implement the stated strict-subset behavior and verify that partial resampling works across all applicable dimensions while existing explicit `dim_names` behavior remains unchanged.

Written by the indexing model from the issue text.