refactor: replace superspawn with execa

[raphinesse]

Motivation and Context

Progresses https://github.com/apache/cordova/issues/16 and https://github.com/apache/cordova/issues/7

Description

Use execa for any subprocess spawning.

A few notes

execa has no equivalent of superspawn's printCommand option (if set to true, it emits a verbose log of the command being executed). In the current state of this PR, those verbose logs are removed without a substitute.

superspawn promises resolve to the captured stdout, while execa resolves to an object with more properties. In many of the cases where we spawn subprocesses, this does not matter, since we we only care about promise fulfillment.

superspawn allowed to subscribe to a running process' output by means of Q's progress method. This basically directly translates to subscribing to data events on the backing streams. So that is what we used to replace these calls. However, the existing code seems to assume that the data emitted are whole lines of output only. This is by no means guaranteed, so we added FIXME comments to the code.

Testing

• Existing tests pass
• It would be great if someone could do some manual tests with the platform (I own no Apple computer)

[codecov-commenter]

Codecov Report

Merging #1190 (b01913e) into master (91d869a) will increase coverage by 0.24%. The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #1190      +/-   ##
==========================================
+ Coverage   74.90%   75.15%   +0.24%     
==========================================
  Files          13       13              
  Lines        1654     1658       +4     
==========================================
+ Hits         1239     1246       +7     
+ Misses        415      412       -3     

Impacted Files	Coverage Δ
bin/templates/scripts/cordova/lib/run.js	23.07% <15.38%> (+0.34%)	:arrow_up:
bin/templates/scripts/cordova/lib/Podfile.js	75.12% <22.22%> (+1.91%)	:arrow_up:
bin/templates/scripts/cordova/lib/build.js	44.44% <50.00%> (+0.34%)	:arrow_up:
bin/templates/scripts/cordova/lib/versions.js	89.36% <92.30%> (+0.98%)	:arrow_up:
bin/templates/scripts/cordova/lib/listDevices.js	100.00% <100.00%> (ø)

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[raphinesse]

Thanks so much for the test!