Color code pinned file item in the file browser

The following discussion from !137544 (merged) should be addressed:

• @danmh started a discussion:

  thought (non-blocking): There is opportunity to use colour to strengthen the link between the pinned file in the file browser and the diff.

  suggestion (non-blocking): you could consider and idea like the following

  Selected file	Not selected file

  I recommend collaborating with @afracazo @mnearents on this in a follow up