Update to latest Fonts and implement upstream clipper fix

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

• Updates Fonts to 1.0.0-beta19.15
• Applies an upstream fix from Clipper2 that further reduced extraneous vertices in solutions.

[codecov]

Codecov Report

Merging #278 (3ba5a75) into main (7b19f39) will decrease coverage by 1%.
The diff coverage is 68%.

@@         Coverage Diff         @@
##           main   #278   +/-   ##
===================================
- Coverage    79%    79%   -1%     
===================================
  Files        97     97           
  Lines      5088   5093    +5     
  Branches    945    947    +2     
===================================
+ Hits       4025   4026    +1     
+ Misses      875    868    -7     
- Partials    188    199   +11     

Flag	Coverage Δ
unittests	79% <68%> (-1%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...arp.Drawing/Shapes/PolygonClipper/ClipperOffset.cs	100% <ø> (ø)
...rp.Drawing/Shapes/PolygonClipper/PolygonClipper.cs	64% <0%> (+<1%)	⬆️
...ImageSharp.Drawing/Shapes/Text/BaseGlyphBuilder.cs	87% <0%> (-2%)	⬇️
....Drawing/Shapes/PolygonClipper/PolygonOffsetter.cs	73% <72%> (-3%)	⬇️
...rocessing/Processors/Text/RichTextGlyphRenderer.cs	95% <100%> (ø)

... and 1 file with indirect coverage changes

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[JimBobSquarePants]

Stupid NET 472 x86!!