Deprecate the box1 box2 arguments to BoxResize.

[joaander]

Description

Add the box argument to BoxResize. Deprecate box1, box2, and variant.

Motivation and context

Box variants provide a more flexible solution.

Resolves #1640

How has this been tested?

Added unit tests.

Change log

Added:

* ``box`` argument to ``hoomd.update.BoxResize`` that accepts a ``BoxVariant``.

Deprecated:

* ``box1``, ``box2``, and ``variant`` arguments to ``hoomd.update.BoxResize``.

Checklist:

• I have reviewed the Contributor Guidelines.
• I agree with the terms of the HOOMD-blue Contributor Agreement.
• My name is on the list of contributors (sphinx-doc/credits.rst) in the pull request source branch.

[tcmoore3]

LGTM!

[tcmoore3]

pytest is failing because variant.box.Interpolate is not pickleable because I didn't add a __reduce__ method in #1736 like I did for variant.box.Constant. I will add one shortly if it's not there before I can get to it.