Extract `ContextHistory` to `assistant_context_editor` (#23437)

This PR extracts the `ContextHistory` to the `assistant_context_editor`
crate.

Release Notes:

- N/A
be407e27f9Marshall Bowers committed on 1/22/2025, 1:32:24 AM· committed by GitHubparente59c910
8 files changedLine totals unavailable