legacy: refacored makeSourceFile / other minor code moved

[cmaglie]

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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?

refacored makeSourceFile / other minor code moved

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: 85.91% and no project coverage change.

Comparison is base (b8024c3) 63.82% compared to head (17defc8) 63.82%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2303   +/-   ##
=======================================
  Coverage   63.82%   63.82%           
=======================================
  Files         214      214           
  Lines       19794    19794           
=======================================
  Hits        12633    12633           
+ Misses       6074     6073    -1     
- Partials     1087     1088    +1     

Flag	Coverage Δ
unit	63.82% <85.91%> (ø)

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

Files Changed	Coverage Δ
arduino/builder/sketch.go	48.95% <ø> (-5.36%)	⬇️
legacy/builder/create_cmake_rule.go	8.30% <0.00%> (ø)
legacy/builder/test/helper_tools_downloader.go	60.80% <0.00%> (ø)
arduino/builder/builder.go	85.18% <82.60%> (-14.82%)	⬇️
arduino/builder/detector/detector.go	74.56% <89.47%> (-0.06%)	⬇️
arduino/builder/utils/utils.go	76.49% <100.00%> (ø)
commands/compile/compile.go	71.34% <100.00%> (-0.09%)	⬇️
legacy/builder/merge_sketch_with_bootloader.go	75.70% <100.00%> (ø)
legacy/builder/phases/core_builder.go	77.77% <100.00%> (ø)
legacy/builder/phases/libraries_builder.go	80.37% <100.00%> (ø)
... and 2 more

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