Support typing into the compltion

[tmcw]

CleanShot.2024-03-25.at.16.54.39.mp4

VS Code lets you do this, as did the plugin that this is modeled after. You type parts of the suggested text and instead of clearing the suggestion, it kind of gradually accepts it.

This was harder to adjust to the Codeium way of doing things, which can include multiple suggestions in a single batch at different parts of the document. But it's good behavior and it'd be nice to bring it back.