Fix Vertical Layout with Custom LineSpacing

[JimBobSquarePants]

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Description

This pull request updates the vertical text layout logic in TextLayout.cs to improve glyph alignment and positioning, particularly when handling line heights and spacing. The changes focus on using unscaled line heights for more accurate centering and resetting horizontal positions more reliably at grapheme boundaries.

Glyph alignment and centering improvements:

• Changed centering calculations in both LayoutLineVertical and LayoutLineVerticalMixed to use unscaledLineHeight instead of scaledMaxLineHeight, resulting in more consistent glyph alignment across different font metrics. [1] [2] [3] [4]

Position reset and state management:

• Introduced lineOriginX to reliably reset boxLocation.X and penLocation.X at grapheme boundaries, ensuring horizontal positions are correctly restored for each new line or grapheme. [1] [2]

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83%. Comparing base (80a0d61) to head (cf8b302).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #500   +/-   ##
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  Coverage     83%     83%           
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  Files        274     274           
  Lines      19184   19184           
  Branches    2719    2719           
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  Hits       16081   16081           
  Misses      2426    2426           
  Partials     677     677           

Flag	Coverage Δ
unittests	83% <100%> (ø)

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