dev!: replace `loginWithPassword` mutation with provider

[justlevine]

What

Removes the loginWithPassword mutation in favor of using a Password provider.

Various method, action, and filter signatures have changed as well.

Why

Better extendability.

How

• feat!: Remove loginWithPassword mutation in favor of Password provider.
• dev!: Refactor ProviderConfig methods.

Testing Instructions

Additional Info

Checklist:

• [x] My code is tested to the best of my abilities.
• [x] My code follows the WordPress Coding Standards.
• [x] My code has proper inline documentation.
• [x] I have added unit tests to verify the code works as intended.
• [x] I included the relevant changes in CHANGELOG.md

[coveralls]

Coverage: 61.084% (+0.5%) from 60.564% when pulling ed1bc710363c854c9011d8644a70cd42cb2cf584 on justlevine:dev/refactor-password-to-provider-config into fdda8f1ce46c394eb9e3a239e0c10f39f6cd971f on AxeWP:develop.