Add a coerce formal charges method to openff code

[orionarcher]

Summary

Major changes:

Add a coerce_formal_charges method to the pymatgen.io.openff code, allowing molecules with formal charges to be more accurately parsed.

Checklist

• Google format doc strings added. Check with ruff.
• Type annotations included. Check with mypy.
• Tests added for new features/fixes.
• If applicable, new classes/functions/modules have duecredit @due.dcite decorators to reference relevant papers by DOI (example)

[shyuep]

Please add a unittest for the new method. Thanks.