[skip-changelog] legacy: some simple refactorings

[cmaglie]

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• The PR has no duplicates (please search among the Pull Requests
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• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)
• configuration.schema.json updated if new parameters are added.

What kind of change does this PR introduce?

Some simple refactorings to legacy package

What is the current behavior?

What is the new behavior?

No changes

Does this PR introduce a breaking change, and is titled accordingly?

Other information

This is part of #1766

[codecov]

Codecov Report

Patch coverage: 82.27% and project coverage change: -0.01 ⚠️

Comparison is base (8310d01) 62.80% compared to head (e6b20fe) 62.80%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2206      +/-   ##
==========================================
- Coverage   62.80%   62.80%   -0.01%     
==========================================
  Files         219      218       -1     
  Lines       19469    19462       -7     
==========================================
- Hits        12228    12223       -5     
+ Misses       6156     6154       -2     
  Partials     1085     1085              

Flag	Coverage Δ
unit	62.80% <82.27%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
legacy/builder/container_find_includes.go	72.02% <79.68%> (+1.74%)	⬆️
legacy/builder/types/types.go	80.00% <83.33%> (+1.87%)	⬆️
arduino/libraries/librarieslist.go	86.11% <100.00%> (ø)
legacy/builder/types/accessories.go	100.00% <100.00%> (+11.76%)	⬆️

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