fix: split diagnostic lines on \n character in floating window

[emgeee]

This PR attempts to help display diagnostic messages in a more graceful way.

Before, newline characters ('\n') in diagnostic messages were simply stripped out. This PR instead writes them out to a separate line

Before

After

Ideally, it'd be nice to not display the horizontal lines so it's more clear certain lines are meant to be grouped together but I wasn't entirely sure how to do that.

Open to feedback!