Fully merge the Watson and Embeddings classification features

[dkotter]

Description of the Change

Historically (though I use that term loosely since the Embeddings functionality hasn't been around that long) we've had two classification Features:

1. Analyze your content and suggest new terms using the Watson API
2. Analyze your content and existing terms, suggesting which of the existing terms are the best match using the OpenAI Embeddings API

Coming out of the work in #611, these two separate features were merged down into a single Feature, with Watson and Embeddings being two different providers for that Feature.

But we left most of the functionality in each individual Provider class instead of bringing that into the Feature class. These features are very similar but have diverged a bit over time so there wasn't an easy, clean merge that could be done.

The ultimate goal was to merge those two together and bring parity between the two and that is what this PR does. All shared functionality has been moved from the individual Provider classes into the Classification Feature class. Any functionality that was missing between the two (like the modal popup we added to Watson but never to Embeddings) has been taken care of. In theory, the Classification Feature should now function basically the same no matter the Provider that is selected.

Closes #671
Closes #699
Closes #714

How to test the Change

I would suggest fully testing the Classification Feature with both Providers. This could involve the following:

• Ensure classifying content works in the Classic Editor, both with the checkbox checked and clicking the classify button
• Ensure classifying content works in the Block Editor, both with the checkbox checked and clicking the classify button
• Ensure classifying an individual item works from the post list screen by clicking the inline link
• Ensure classifying one or more items works from the post list screen by using the bulk actions dropdown

Changelog Entry

Added - Ability to preview which terms will be added before they get added when using the Embeddings provider.
Changed - Ensure the Classification functionality works the same for all Providers.
Fixed - Fix fatal error if both the Classification Feature and Moderation Features are active.

Credits

Props @dkotter

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[iamdharmesh]

@dkotter, Thanks a lot for merging this. The code LGTM and it tests well. However, I have added two minor suggestions; otherwise, everything looks good.

Also, I have noticed that when we use embeddings as a provider, it also suggests the 'Uncategorized' category as a matching term. I'm not sure if this happens in my setup only. Could you please check once? If it suggests 'Uncategorized,' then we might want to filter it from the suggestions list.

[dkotter]

Also, I have noticed that when we use embeddings as a provider, it also suggests the 'Uncategorized' category as a matching term. I'm not sure if this happens in my setup only. Could you please check once? If it suggests 'Uncategorized,' then we might want to filter it from the suggestions list

Saw the same thing. This should now be excluded

[iamdharmesh]

LGTM 🚀

@dkotter I have added 2 minor commits to fix #714 and Exclude the "Post Format" taxonomy from the supported taxonomies list. This is ready to merge now. Thank you.