[PATCH RFC 0/20] cat-file: start using formatting logic from ref-filter

Hi everyone, It was a long way for me, I got older (by 1 year) and smarter (hopefully), and maybe I will finish my Outreachy Internship task for now. (I am doing it just for one year and a half, that's OK)

If serious: In this patch we remove cat-file formatting logic and reuse ref-filter logic there. As a positive side effect, cat-file now has many new formatting tokens (all from ref-filter formatting), including deref (like %(*objectsize:disk)). I have already tried to do this task one year ago, and it was bad attempt. I feel that today's patch is much better.

In my opinion, it still has some issues. I mentioned all of them in TODOs in comments. All of them considered to be separate tasks for other patches. Some of them sound easy and could be great tasks for newbies.

I also have a question about site https://git-scm.com/docs/ I thought it is updated automatically based on Documentation folder in the project, but it is not true. I edited docs for for-each-ref in December, I still see my patch in master, but for-each-ref docs in git-csm is outdated. Is it OK?

Thank you! Olga