[breaking] Improved .pde warnings detection subroutines / gRPC LoadSketch API improvement

[cmaglie]

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• The PR has no duplicates (please search among the Pull Requests
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• The PR follows
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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?

• The .pde deprecation warning is printed only when the sketch is valid.
• The scanning for pde files has been optimized
• The gRPC API about LoadSketch has been improved as well as part of the refactoring.

What is the current behavior?

$ arduino-cli compile -b arduino:avr:uno
Sketches with .pde extension are deprecated, please rename the following files to .ino:
 - /home/megabug/Workspace/arduino-cli/internal/arduino/builder/testdata/TestLoadSketchFolder/old.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/builder/testdata/TestLoadSketchFolderBothInoAndPde/TestLoadSketchFolderBothInoAndPde.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/builder/testdata/TestLoadSketchFolderBothInoAndPde/old.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/builder/testdata/TestLoadSketchFolderPde/TestLoadSketchFolderPde.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/builder/testdata/TestLoadSketchFolderPde/old.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/builder/testdata/TestLoadSketchFolderSymlinkSrc/old.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/libraries/testdata/TestLibExamples/examples/MultipleFiles/MultipleFiles.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/sketch/testdata/SketchBothInoAndPde/SketchBothInoAndPde.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/sketch/testdata/SketchMultipleMainFiles/SketchMultipleMainFiles.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/sketch/testdata/SketchPde/SketchPde.pde
 - /home/megabug/Workspace/arduino-cli/internal/arduino/sketch/testdata/SketchSymlinkSrc/old.pde
 - /home/megabug/Workspace/arduino-cli/internal/integrationtest/compile_4/testdata/SketchWithMergedSketchAndBootloader/old.pde
 - /home/megabug/Workspace/arduino-cli/internal/integrationtest/testdata/sketch_multiple_main_files/sketch_multiple_main_files.pde
 - /home/megabug/Workspace/arduino-cli/internal/integrationtest/testdata/sketch_pde_main_file/sketch_pde_main_file.pde
 - /home/megabug/Workspace/arduino-cli/internal/integrationtest/testdata/sketch_simple/old.pde
Can't open sketch: main file missing from sketch: /home/megabug/Workspace/arduino-cli/arduino-cli.ino
$

The pde warnings are printed even if the current directory is not a valid sketch.

What is the new behavior?

$ arduino-cli compile -b arduino:avr:uno
Can't open sketch: main file missing from sketch: /home/megabug/Workspace/arduino-cli/arduino-cli.ino
$

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

Yes, there is a breaking change in the gRPC API.

Other information

Fix #2384

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (95753fc) 68.85% compared to head (173f8bc) 68.80%.

Files	Patch %	Lines
internal/cli/upload/upload.go	50.00%	2 Missing and 1 partial ⚠️
commands/instances.go	50.00%	1 Missing and 1 partial ⚠️
internal/cli/arguments/sketch.go	66.66%	1 Missing and 1 partial ⚠️
commands/daemon/daemon.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2490      +/-   ##
==========================================
- Coverage   68.85%   68.80%   -0.05%     
==========================================
  Files         204      204              
  Lines       20465    20443      -22     
==========================================
- Hits        14091    14066      -25     
- Misses       5220     5222       +2     
- Partials     1154     1155       +1     

Flag	Coverage Δ
unit	68.80% <89.74%> (-0.05%)	⬇️

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