This PR extracts the `PromptLibrary` out of the `assistant` crate and
moves it to the `prompt_library` crate.
The `PromptLibrary` is now decoupled from the specifics of the
`AssistantPanel` and `InlineAssistant`.
Release Notes:
- N/A
This PR adds a new `prompt_library` crate and extracts the `PromptStore`
and `PromptBuilder` to it.
Eventually we'll want to house the `PromptLibrary` itself in this crate,
but right now that involves untangling a few dependencies.
Release Notes:
- N/A
Piotr Osiewicz
Marshall Bowers