gRPC: if an Upload request is canceled, immediately terminate the upload tool process.

[cmaglie]

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• Tests for the changes have been added (for bug fixes / features)
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What kind of change does this PR introduce?

If an Upload gRPC request is canceled, the underlying upload tool is terminated immediately.
In particular, this affects the Arduino IDE "cancel" button, because the IDE can only cancel the Upload gRPC request and has no control over the underlying upload tool.

What is the current behavior?

If an Upload gRPC request is canceled, the underlying upload tool is NOT terminated, and it may take a very long time to timeout and close itself.

What is the new behavior?

The upload tool is terminated immediately.

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

Other information

Related to:

• Canceling compilation or upload doesn't kill tool process arduino-ide#2517
• Allow user to terminate compilation and upload processes arduino-ide#1199

[codecov]

Codecov Report

Attention: Patch coverage is 32.35294% with 23 lines in your changes missing coverage. Please review.

Project coverage is 67.66%. Comparing base (ac6ec6d) to head (5bbbe80).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/mock_avrdude/main.go	0.00%	18 Missing ⚠️
commands/service_upload.go	68.75%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2726      +/-   ##
==========================================
- Coverage   67.68%   67.66%   -0.03%     
==========================================
  Files         234      235       +1     
  Lines       22285    22314      +29     
==========================================
+ Hits        15083    15098      +15     
- Misses       6017     6031      +14     
  Partials     1185     1185              

Flag	Coverage Δ
unit	67.66% <32.35%> (-0.03%)	⬇️

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[alessio-perugini]

Nice one! LGTM.