Measure a run's advance with its own font

[splitbrain]

The word break between two runs on a line is decided by the gap between them minus the advance width of the first run. That advance was measured with the font of the second run, so on a line that changes font mid-way the glyph widths of the wrong font were used and a space appeared or went missing. Each run's font is now carried to the next iteration and used to measure its own advance.

Six samples change, all on lines that switch font. Words that were run together or split apart are now separated correctly: "accusamusEt", "perspiciatisQuo" and "debitisQui" in gdocs-lorem-ipsum-with-titles-and-formatting, and the product name "VistalinkTM" in text-objects-across-multiple-streams, which was split into "Vista linkTM" twice.

The spacing around punctuation shifts either way: three spaces before a full stop disappear in word365-lorem-ipsum-with-titles-and-formatting, one appears in issue-457 and one in issue-235. In issue-457 the formula "x + y = 56" loses two spaces: the "+" and "=" are OpenSymbol glyphs whose advance includes wide side bearings, so the gap left over is smaller than the word break threshold once the advance is measured with the font that actually draws them.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.90%. Comparing base (1dffdf9) to head (4f81779).

Files with missing lines	Patch %	Lines
src/Extraction/Markdown/MarkdownExtractor.php	0.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #514      +/-   ##
============================================
- Coverage     49.94%   49.90%   -0.05%     
- Complexity     1874     1875       +1     
============================================
  Files           108      108              
  Lines          3588     3591       +3     
============================================
  Hits           1792     1792              
- Misses         1796     1799       +3     

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[PrinsFrank]

Thank you!!