ensure we can disable --track-widget-creation in debug mode

[jonahwilliams]

Description

Though it is still on by default, allow it to be toggled off.

Fixes #43014

[codecov]

Codecov Report

Merging #43016 into master will increase coverage by 0.31%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #43016      +/-   ##
==========================================
+ Coverage   60.55%   60.86%   +0.31%     
==========================================
  Files         195      195              
  Lines       18940    18940              
==========================================
+ Hits        11469    11528      +59     
+ Misses       7471     7412      -59

Flag	Coverage Δ
#flutter_tool	60.86% <100%> (+0.31%)	⬆️

Impacted Files	Coverage Δ
...utter_tools/lib/src/build_system/targets/dart.dart	47% <100%> (+0.53%)	⬆️
packages/flutter_tools/lib/src/bundle.dart	85.71% <100%> (+0.25%)	⬆️
...s/flutter_tools/lib/src/test/flutter_platform.dart	0.55% <0%> (-27.5%)	⬇️
...ackages/flutter_tools/lib/src/commands/unpack.dart	6.49% <0%> (-24.68%)	⬇️
packages/flutter_tools/lib/src/version.dart	93.23% <0%> (-1.94%)	⬇️
packages/flutter_tools/lib/src/vmservice.dart	40.83% <0%> (-1%)	⬇️
packages/flutter_tools/lib/src/cache.dart	48.47% <0%> (-0.71%)	⬇️
...ages/flutter_tools/lib/src/base/user_messages.dart	51.35% <0%> (+0.9%)	⬆️
packages/flutter_tools/lib/src/run_cold.dart	43.52% <0%> (+1.17%)	⬆️
packages/flutter_tools/lib/src/codegen.dart	7.04% <0%> (+1.4%)	⬆️
... and 11 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1982a5c...1d2606b. Read the comment docs.

[jacob314]

Great to see this enabled by default with an escape hatch.