add accessor convert to base units

[kgoebber]

Description Of Changes

This PR adds to the metpy xarray accessor to have a convert_to_base_units() function, which will allow for the simplification of complex units following calculations using quantify xarray DataArrays.

Added a test and a simple example to the xarray tutorial.

Checklist

• Closes add xarray accessor interface for to_base_units #2363
• Tests added
• Fully documented

[dopplershift]

Looks good to me. @jthielen how do you feel about the spelling of this? It doesn't look like pint-xarray has a corresponding method for us to match.

[dopplershift]

We can ignore Codacy here. I keep trying to get it to set the "issue" as ignored, but every analysis keeps flagging it.

[jthielen]

@jthielen how do you feel about the spelling of this? It doesn't look like pint-xarray has a corresponding method for us to match.

Yep, I noticed that as well, though I would suspect that if it ever did get added it would be consistent with the underlying Pint method of to_base_units. For now, having convert_to_base_units as this PR has now seems best for consistency with our other existing methods. But, if we did want to make the switch at this point to having more Pint-like to, etc. as preferred, then I guess we could just go with to_base_units and avoid introducing another aliased method.

[jthielen]

Looks good to me (pending decision on method name)!

[dopplershift]

Until there's actually something to be consistent with elsewhere, we shouldn't invent something that may be consistent with it. So given that the current naming fits with our existing API, that's what seems to be best for our users.