Add hatch pattern brushes and reference images

[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

Add a new large collection of 8x8 boolean hatch masks (derived from GDI+ pixel extraction technique) to provide many hatch patterns. Fixes incorrectly implemented existing pattern brushes.

[codecov]

Codecov Report

❌ Patch coverage is 93.16860% with 47 lines in your changes missing coverage. Please review.
✅ Project coverage is 86%. Comparing base (c063e6c) to head (dd661f6).

Files with missing lines	Patch %	Lines
src/ImageSharp.Drawing/Processing/Brushes.cs	55%	47 Missing ⚠️

Additional details and impacted files

@@         Coverage Diff          @@
##           main   #393    +/-   ##
====================================
  Coverage    85%    86%            
====================================
  Files       108    109     +1     
  Lines      8421   9052   +631     
  Branches   1085   1085            
====================================
+ Hits       7236   7820   +584     
- Misses      935    982    +47     
  Partials    250    250            

Flag	Coverage Δ
unittests	86% <93%> (+<1%)	⬆️

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