Show whitespace message when there's nothing to show

What does this MR do and why?

Show whitespace message when there's nothing to show

An empty table was rendered, when diff consistent only of whitespace changes and Hide whitespace changes was selected. Detecting the whitespace changes allows to render a message identical to what we have in the new rapid diff implementation.

Changelog: fixed

References

Screenshots or screen recordings

Context	Before	After
hide whitespace
show whitespace

How to set up and validate locally

1. Go to a project
2. Create a commit to any of your files that only includes whitespace changes (one extra space in one of the lines is enough)
3. Go to the commit you've created, for example http://gdk.test:8080/flightjs/Flight/-/commit/[SHA_OF_YOUR_COMMIT]
4. Scroll down to the files and make sure you see the message about only whitespace changes after you choose Hide whitespace changes

MR acceptance checklist

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Related to #570565