Remove ephemeral directories during flutter clean

[jmagman]

Description

Remove ephemeral directories used by modules during flutter clean

Related Issues

Fixes #37909.

Tests

Updated "removes build and .dart_tool and ephemeral directories"

Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I signed the [CLA].
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

• Yes, this is a breaking change (Please read [Handling breaking changes]). Replace this with a link to the e-mail where you asked for input on this proposed change.
• No, this is not a breaking change.

[jonahwilliams]

LGTM

[codecov]

Codecov Report

Merging #37966 into master will increase coverage by 1.3%.
The diff coverage is 91.42%.

@@            Coverage Diff            @@
##           master   #37966     +/-   ##
=========================================
+ Coverage   54.74%   56.05%   +1.3%     
=========================================
  Files         194      194             
  Lines       18170    18169      -1     
=========================================
+ Hits         9948    10185    +237     
+ Misses       8222     7984    -238

Flag	Coverage Δ
#flutter_tool	56.05% <91.42%> (+1.3%)	⬆️

Impacted Files	Coverage Δ
packages/flutter_tools/lib/src/commands/clean.dart	95.23% <100%> (+17.96%)	⬆️
packages/flutter_tools/lib/src/project.dart	81.87% <86.36%> (ø)	⬆️
...kages/flutter_tools/lib/src/commands/precache.dart	50% <0%> (-41.67%)	⬇️
packages/flutter_tools/lib/src/version.dart	90.73% <0%> (-1.96%)	⬇️
packages/flutter_tools/lib/src/device.dart	55.42% <0%> (-1.81%)	⬇️
packages/flutter_tools/lib/src/cache.dart	41.74% <0%> (-0.98%)	⬇️
...utter_tools/lib/src/build_system/build_system.dart	93.01% <0%> (+0.53%)	⬆️
packages/flutter_tools/lib/src/base/process.dart	80.46% <0%> (+0.78%)	⬆️
packages/flutter_tools/lib/src/base/os.dart	29.83% <0%> (+1.61%)	⬆️
packages/flutter_tools/lib/src/template.dart	96.66% <0%> (+1.66%)	⬆️
... and 12 more

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[zanderso]

nit: flip the sense of the if and un-indent, like:

if (!file.existsSync()) {
  return;
}
try {
  ...
}
...

you might also move the printStatus() after checking that the object exists.