Highlight text for AI inline edits

[mscolnick]

Description

We want users to be able to select text in a cell and ask an AI-assist to change that code. It should be similar logic to how AI-assist edits full cells but instead the line(s) selection for the cell

Suggested solution

This should be a codemirror plugin paired with the existing AI /completions endpoint.

Alternative

No response

Additional context

No response