Avoid bundling DOM-related code in the built pdf.worker.mjs file

[Snuffleupagus]

Currently the isCanvasFilterSupported/isAlphaColorInputSupported getters, on the FeatureTest class, contains code that cannot run in the worker-thread since it relies on the DOM being available.
To avoid that a new DEFINE is added, in gulpfile.mjs, to allow skipping this sort of dead code in the built pdf.worker.mjs file.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 14.28571% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.17%. Comparing base (bf9ae76) to head (204f920).

Files with missing lines	Patch %	Lines
src/shared/util.js	14.28%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21269      +/-   ##
==========================================
+ Coverage   54.70%   56.17%   +1.46%     
==========================================
  Files         216      220       +4     
  Lines       59131    59234     +103     
==========================================
+ Hits        32347    33274     +927     
+ Misses      26784    25960     -824     

Flag	Coverage Δ
fonttest	8.64% <0.00%> (?)
unittest	55.45% <0.00%> (?)
unittestcli	54.70% <14.28%> (+<0.01%)	⬆️

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[Snuffleupagus]

/botio browsertest

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Received

Command cmd_browsertest from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.241.84.105:8877/94964f75c1f8b4f/output.txt

[moz-tools-bot]

From: Bot.io (Windows)

---

Received

Command cmd_browsertest from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.193.163.58:8877/7b8a6eb374a2e50/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Failed

Full output at http://54.241.84.105:8877/94964f75c1f8b4f/output.txt

Total script time: 18.30 mins

• Regression tests: FAILED

  different ref/snapshot: 1

Image differences available at: http://54.241.84.105:8877/94964f75c1f8b4f/reftest-analyzer.html#web=eq.log

[timvandermeij]

r=me; thank you for improving this!

[moz-tools-bot]

From: Bot.io (Windows)

---

Failed

Full output at http://54.193.163.58:8877/7b8a6eb374a2e50/output.txt

Total script time: 24.53 mins

• Regression tests: FAILED

  different ref/snapshot: 1

Image differences available at: http://54.193.163.58:8877/7b8a6eb374a2e50/reftest-analyzer.html#web=eq.log