Render placeholder for added and removed empty files in Rapid Diffs

Stanislav Lashmanovrequested to merge
slashmanov/rapid-diffs-empty-file into master

What does this MR do and why?

This MR adds placeholders was added and removed empty files to Rapid Diffs.

Screenshots or screen recordings

Before After
image image

How to set up and validate locally

  1. Enable rapid_diffs_on_compare_show feature flag
  2. Open compare revisions page for a branch with empty added or removed file
  3. Observe new placeholder

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