Start adding UI to AI text provider API

[andreamah]

Addresses #205317

These are the first steps to integrating the UI for the AI text results. All of this UI will still be inaccessible by users after this is merged, as the actions to enable the context key is behind a hidden button.

I still need to implement some pretty glaring things like:

• changing the result count.
• having the extension automatically activate.
• overall perf

I want to shift to cleaning up the search model for multiple "match types", since the addition of AI matches makes the search model even messier than before. The search model's current structure makes it hard to add new types.