Cannot cancel an inline code generation

On VSCode

## Problem

The main issue is that when generating inline code in a file (through Cmd+I), we can't stop it until it is done.

What makes it worse is the underlaying model liking to rewrite the entire file instead of just inserting the few lines requested.

Final result is having to wait a full minute for the LLM to rewrite the whole file in a function just to add a single line of new code.

## Expected behavior

Next to the "Generating" inline text, have a "Cancel" button enabling us to stop and remove the generated code. And even a "Stop" button to just pick the line we need and cancel right after.

Start by tracing the VSCode inline code-generation flow invoked through Cmd+I, focusing on how the “Generating” state and generated edits are managed. Determine how cancellation should remove partial output and clarify whether the proposed Stop behavior is in scope; done means generation can be cancelled without leaving unwanted generated code.

Written by the indexing model from the issue text.