Prepend bold/italic styles for XHTML B/I elements (issue 22023)

[cestercian]

B and I called measure.pushFont() in $pushGlyphs, but TextMeasure never had that method, so laying out rich text with <b> or <i> in an auto-sized field threw and the whole form failed to render.

Following the shorter approach from #22023 (comment): prepend font-weight:bold / font-style:italic in the B and I constructors (so explicit styles like font-weight:normal still win) and drop their $pushGlyphs overrides, letting the existing XhtmlObject path handle measurement and rendering.

Added a unit test with bold and italic rich text in a draw without a height; it fails without the change.

Fixes #22023

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.17%. Comparing base (17bb244) to head (11e274b).
⚠️ Report is 55 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #22083      +/-   ##
==========================================
- Coverage   90.30%   90.17%   -0.13%     
==========================================
  Files         269      275       +6     
  Lines       67362    67833     +471     
==========================================
+ Hits        60828    61166     +338     
- Misses       6534     6667     +133     

Flag	Coverage Δ
browsertest	66.18% <0.00%> (+0.10%)	⬆️
fonttest	8.98% <ø> (+0.02%)	⬆️
integrationtest	69.22% <0.00%> (-0.01%)	⬇️
unittest	60.06% <100.00%> (+0.18%)	⬆️
unittestcli	58.43% <100.00%> (+0.01%)	⬆️

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[Snuffleupagus]

#22023 (comment) outlines a another possible, and shorter, solution. Would that work instead?

[cestercian]

@Snuffleupagus Good call, thanks. Switched to the shorter style-prepend approach from that issue comment: B/I constructors now prepend font-weight:bold / font-style:italic and the $pushGlyphs overrides (and the TextMeasure.pushFont idea) are gone.

[github-actions]

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