Syntax highlighting for diff hunks

[eseliger]

Implement syntax highlighting for diff hunks. As we use diff views more and more with campaigns really coming together, I'm feeling that proper syntax highlighting here would add a ton of value.

While hacking something together using highlightjs in the DiffHunk component, it became clear that this adds a high value in legibility.

Before:

After:

[slimsag]

This should really be done with our backend syntax highlighter and not highlightjs

[eseliger]

That’s the plan the screenshot was just to verify how much value it adds

[mrnugget]

I'll take this on in 3.16, timeboxed, because I'm not sure yet what's involved.