Add hook to pretty print code to show in diff in pull requests

**Is your feature request related to a problem? Please describe.**
I often work in ABAP, which is case insensitive, and my diffs are often noisy:


I would like to add a pretty printer hook to atlascode so I can mask most of the irrelevant differences:


Another use case could be for instance unminifying javascript, or format and sort json

was https://bitbucket.org/atlassianlabs/atlascode/issues/5433/add-hook-to-pretty-print-code-to-show-in

**Describe the solution you'd like**
See the diff between formatted code rather than raw
I do want the ability to see the raw diff, just not as the default
Formatter is provided by another, language specific extension

I already have this working, will send a PR soon

**Describe alternatives you've considered**
Postprocess in my extension: works but I lose commenting and stuss like that

**Additional context**
Add any other context or screenshots about the feature request here.

No repository files, tests, or entry points are named. Start by tracing atlascode’s pull-request diff rendering and the integration point for language-specific formatters; done means formatted diffs are the default, raw diffs remain selectable, and commenting still works.

Written by the indexing model from the issue text.