This PR ensures truncation works for the file paths, which should set up
the stage for when the new GPUI `truncation_start` method lands
(https://github.com/zed-industries/zed/pull/45122) so that we can use
for them. In the process of doing so and figuring it out why it wasn't
working as well before, I noticed some opportunities to clean up some UI
code: removing unnecessary styles, making the file easier to navigate
given all of the different UI conditions, etc.

Note: You might notice a subtle label flashing that comes with the label
truncation and that's a standalone GPUI bug that's also visible in other
surface areas of the app. I don't think it should block these changes
here as it's something we should fix on its own...

Release Notes:

- N/A