Ignore empty hover contents, trim final hover label text (#2747)

Removes empty hovers from appearing:

![image](https://github.com/zed-industries/zed/assets/2690773/b8a8af17-e20f-4d87-8782-465dfbf9b561)

And trims final hover label to ensure no trailing whitespaces are
present:

![image](https://github.com/zed-industries/zed/assets/2690773/24aeb0f0-d4f0-4e2b-9265-53694bfec437)


Release Notes:

- Tidies up hover elements by trimming them and removing the empty ones