Dry up rendering code

[theteachr]

Cleans up the duplication that was introduced by #5318.

[theteachr]

Is render_buffer_title a better name?

[the-mikedavis]

I still like render_path. I don't see the file path as the title of the buffer (I'm probably biased from the implementation 😅)

Actually we might want to take #4731 instead of this: separating the file modification indicator into its own element reduces the duplication between these two statusline elements and fixes some UI issues

[theteachr]

separating the file modification indicator into its own element

I was planning to work on this next (thanks for the heads up on #4731), as my first priority was to remove the duplication I'd caused.