[ENH] Mask support for regridding

Currently, the internal/SciPy regridding adapters do not support masks (as implemented in !260 (merged)).

Potential solutions to support masks here:

• During initialization/connect, regrid the input mask (0/1). Mask the output where the result is >0. Does not allow for dynamic masks.
• Fill masked data with NaN before regridding. Use NaNs in the output to derive the mask. Allows for dynamic masks.

Not sure about the possibilities for the ESMF regridders.