refactor(xerrors): test error by `errors.Is` and `errors.As`

[wenchy]

• [ ] close #74

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 35.40373% with 312 lines in your changes missing coverage. Please review.

Project coverage is 65.49%. Comparing base (828caa0) to head (6f54a64). Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/confgen/parser.go	7.01%	53 Missing :warning:
xerrors/stack.go	46.51%	43 Missing and 3 partials :warning:
xerrors/errors.go	75.77%	32 Missing and 7 partials :warning:
internal/protogen/parser.go	0.00%	29 Missing :warning:
internal/confgen/document_parser.go	4.34%	22 Missing :warning:
internal/protogen/protogen.go	0.00%	18 Missing :warning:
internal/importer/xml.go	0.00%	14 Missing :warning:
internal/importer/csv.go	0.00%	12 Missing :warning:
internal/importer/excel.go	0.00%	11 Missing :warning:
xerrors/ecode.go	0.00%	9 Missing :warning:
... and 21 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #75      +/-   ##
==========================================
+ Coverage   65.47%   65.49%   +0.01%     
==========================================
  Files          73       74       +1     
  Lines        7757     7990     +233     
==========================================
+ Hits         5079     5233     +154     
- Misses       2102     2172      +70     
- Partials      576      585       +9     

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