Yaml: revise Ypath API

[masatake]

The code for utilizing libyaml in the OpenAPI parser is good enough.
This pull request moves the code to the Yaml Meta parser as Ypath API.

For evaluating the API, this pull request also applies the API to the AnsiblePlaybook parser.

This pull request is a preparation step for merging #3258.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (184d474) 85.05% compared to head (6e5576a) 85.02%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3842      +/-   ##
==========================================
- Coverage   85.05%   85.02%   -0.03%     
==========================================
  Files         228      228              
  Lines       53982    53897      -85     
==========================================
- Hits        45915    45828      -87     
- Misses       8067     8069       +2     

Files	Coverage Δ
parsers/ansibleplaybook.c	100.00% <100.00%> (ø)
parsers/openapi.c	100.00% <ø> (ø)
parsers/yamlfrontmatter.c	100.00% <ø> (+1.66%)	⬆️
parsers/yaml.c	95.80% <97.01%> (-1.51%)	⬇️

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