Add supported charge methods to API

[mattwthompson]

Implements #1830

In [1]: from openff.toolkit.utils import *

In [2]: for _class in GLOBAL_TOOLKIT_REGISTRY.registered_toolkits:
   ...:     print(_class.__class__.__name__, _class.supported_charge_methods)
   ...:
OpenEyeToolkitWrapper ['am1bcc', 'am1-mulliken', 'gasteiger', 'mmff94', 'am1bccnosymspt', 'am1elf10', 'am1bccelf10']
RDKitToolkitWrapper ['mmff94', 'gasteiger']
AmberToolsToolkitWrapper ['am1bcc', 'am1-mulliken', 'gasteiger']
BuiltInToolkitWrapper ['zeros', 'formal_charge']

In [3]: from openff.toolkit import Molecule

In [4]: molecule = Molecule.from_smiles("CCO")

In [5]: molecule.get_available_charge_methods()
Out[5]:
['am1elf10',
 'am1bccelf10',
 'zeros',
 'am1bcc',
 'gasteiger',
 'am1-mulliken',
 'am1bccnosymspt',
 'formal_charge',
 'mmff94']

In [6]: from openff.toolkit.utils.nagl_wrapper import NAGLToolkitWrapper

In [7]: NAGLToolkitWrapper().supported_charge_methods
Out[7]: ['openff-gnn-am1bcc-0.0.1-alpha.1.pt', 'openff-gnn-am1bcc-0.1.0-rc.1.pt']

• Tag issue being addressed
• Add tests
• Update docstrings/documentation, if applicable
• Lint codebase
• Update changelog

[codecov]

Codecov Report

Merging #1834 (d9cd9b0) into main (858d55e) will decrease coverage by 0.01%.
The diff coverage is 96.15%.

❗ Current head d9cd9b0 differs from pull request most recent head 81e14e0. Consider uploading reports for the commit 81e14e0 to get more accurate results

Additional details and impacted files

[j-wags]

I generally like the structure and goals of this PR. Only blocking point is whether this needs to be an API break. It's possible I'm overlooking something but let's discuss on that review comment.

[j-wags]

(blocking) Would it be possible to leave this as SUPPORTED_CHARGE_METHODS to avoid an API change?

[mattwthompson]

I can maintain the API at the cost of duplicated code

[mattwthompson]

I've made an attempt to do that - unfortunately the wrappers disagree on what to call this attribute, so it's not easy to move it into the base class

[j-wags]

Awesome, thanks @mattwthompson! Please update the releasenotes before you merge 🚀

[mattwthompson]

@j-wags just noting here that these have different names; I think there's okay reason for it