legacy: Builder refactorization (part 3...)

[alessio-perugini]

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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?

Refactoring the legacy builder.

What is the current behavior?

What is the new behavior?

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

Other information

[codecov]

Codecov Report

Patch coverage: 82.20% and project coverage change: +0.18% 🎉

Comparison is base (65915d8) 63.82% compared to head (227dbd1) 64.00%.

❗ Current head 227dbd1 differs from pull request most recent head a38853b. Consider uploading reports for the commit a38853b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2302      +/-   ##
==========================================
+ Coverage   63.82%   64.00%   +0.18%     
==========================================
  Files         214      214              
  Lines       19794    19920     +126     
==========================================
+ Hits        12633    12750     +117     
- Misses       6073     6079       +6     
- Partials     1088     1091       +3     

Flag	Coverage Δ
unit	64.00% <82.20%> (+0.18%)	⬆️

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

Files Changed	Coverage Δ
legacy/builder/types/context.go	91.89% <ø> (+0.51%)	⬆️
legacy/builder/create_cmake_rule.go	7.77% <14.81%> (-0.54%)	⬇️
legacy/builder/merge_sketch_with_bootloader.go	74.75% <42.85%> (-0.95%)	⬇️
legacy/builder/container_build_options.go	62.50% <68.18%> (-17.50%)	⬇️
.../builder/warn_about_arch_incompatible_libraries.go	78.57% <75.00%> (-3.79%)	⬇️
commands/compile/compile.go	71.82% <80.95%> (+0.47%)	⬆️
legacy/builder/load_previous_build_options.go	72.72% <83.33%> (-2.28%)	⬇️
legacy/builder/recipe_runner.go	76.31% <83.33%> (+1.31%)	⬆️
legacy/builder/create_build_options_map.go	80.76% <86.95%> (+14.10%)	⬆️
legacy/builder/builder.go	91.53% <96.21%> (+2.06%)	⬆️
... and 6 more

... and 1 file with indirect coverage changes

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[cmaglie]

👍🏼 I've found just a nit