Prevent inherited spacing from affecting text layer

[danyalahmed1995]

Summary

Fixes #21259.

This prevents inherited letter-spacing and word-spacing from affecting the text layer. External page styles can otherwise change the rendered width/positioning of text-layer spans while the PDF canvas remains unchanged, causing text selection/highlight alignment issues.

The fix resets spacing on:

• .textLayer
• the hidden measurement canvas used by the text layer

A regression test was added to cover inherited spacing from the viewer container.

Testing

• npx eslint src/display/text_layer.js test/integration/text_layer_spec.mjs
• npx stylelint web/text_layer_builder.css
• npx gulp generic
• Manual verification in the local viewer:
  • applied letter-spacing: 5px and word-spacing: 5px to body / #mainContainer
  • confirmed body had inherited spacing
  • confirmed .textLayer and text-layer spans stayed at neutral computed spacing
  • confirmed text selection remained aligned

Note: I also tried npx gulp integrationtest --headless --noFirefox -t text_layer, but it did not stay limited to the text-layer test and started running unrelated integration tests, so I stopped it locally.

[timvandermeij]

Looks good to me, with the comment addressed and passing tests. Thank you for your contribution!

[timvandermeij]

Could you squash the commits into one, see https://github.com/mozilla/pdf.js/wiki/Squashing-Commits, and include (a summary of) the context from the PR description in the actual commit message so that it's also clear from e.g. git log what the patch is about? After that I'll trigger the tests here.

[danyalahmed1995]

Sure , give me a moment

[danyalahmed1995]

@timvandermeij Squashed into one commit with the PR context included in the commit message.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.41%. Comparing base (ea18e73) to head (4ee9c39).
⚠️ Report is 22 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21321      +/-   ##
==========================================
+ Coverage   81.39%   81.41%   +0.01%     
==========================================
  Files         256      257       +1     
  Lines       65337    65339       +2     
==========================================
+ Hits        53183    53196      +13     
+ Misses      12154    12143      -11     

Flag	Coverage Δ
fonttest	9.11% <ø> (-0.01%)	⬇️
integrationtest	66.99% <ø> (+0.01%)	⬆️
unittest	56.85% <ø> (+<0.01%)	⬆️
unittestcli	56.06% <ø> (+<0.01%)	⬆️

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[timvandermeij]

/botio-linux preview

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Received

Command cmd_preview from @timvandermeij received. Current queue size: 0

Live output at: http://54.241.84.105:8877/0e9ab44fdd528b3/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Success

Full output at http://54.241.84.105:8877/0e9ab44fdd528b3/output.txt

Total script time: 1.20 mins

Published

• Viewer: http://54.241.84.105:8877/0e9ab44fdd528b3/web/viewer.html
• Viewer (legacy): http://54.241.84.105:8877/0e9ab44fdd528b3/legacy/web/viewer.html

[timvandermeij]

/botio browsertest

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Received

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

Live output at: http://54.241.84.105:8877/0089e6b5470a51d/output.txt

[moz-tools-bot]

From: Bot.io (Windows)

---

Received

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

Live output at: http://54.193.163.58:8877/5a0bdd56e8589f3/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Success

Full output at http://54.241.84.105:8877/0089e6b5470a51d/output.txt

Total script time: 18.28 mins

• Regression tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

---

Success

Full output at http://54.193.163.58:8877/5a0bdd56e8589f3/output.txt

Total script time: 25.32 mins

• Regression tests: Passed

[calixteman]

LGTM. Thank you.