[WIP] support auto anchor option

[goccy]

resolve #461

yaml.UseAutoAnchor() option automatically assigns an anchor name to a value when the same pointer address is found during encoding and uses an alias for reference points

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Codecov Report

Attention: Patch coverage is 78.28571% with 38 lines in your changes missing coverage. Please review.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #606      +/-   ##
==========================================
- Coverage   77.21%   77.19%   -0.03%     
==========================================
  Files          22       22              
  Lines        7870     7966      +96     
==========================================
+ Hits         6077     6149      +72     
- Misses       1374     1393      +19     
- Partials      419      424       +5     

[bep]

@goccy This is a great option that I (and I suspect many others) would really want, I don't see how it fixes #461.

The printing problem I'm talking about isn't (just) marshaling it back to YAML. There's a lot of potential printing going on in Hugo. E.g. to JSON, or templates:

{{ range $k, $v := $frontmatter }}
   {{ printf "%s: %s" $k $v }}
{{ end }}

So what I had in mind was an option to detect malicious/insensible YAML documents and throw an error. I have reopened the upstream PR about this gohugoio/hugo#13033 -- I'm thinking it should be possible to add some "sanity checks" on the unmarshaled Go map.

But again, an auto anchor option is still a great idea.

[goccy]

This feature has already been supported by #662 , so close this PR.