add from_mbuild function

[mikemhenry]

Description

mBuild has some nice lattice building tooling that would be nice to use with interchange.

[mattwthompson]

Part of this exists here (Foyer ingesting OpenFF topologies): https://github.com/mosdef-hub/foyer/blob/9c564385fb2106229a406173ec276bcdbd15ee61/foyer/topology_graph.py#L166

Implementing this without a force field would look like:

openff-interchange/openff/interchange/components/toolkit.py

Line 108 in 8d2cee1

def _simple_topology_from_openmm(openmm_topology: "openmm.app.Topology") -> Topology: