Update Fonts Reference and Introduce Shared TextOptions

[JimBobSquarePants]

Prerequisites

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

Description

Fixes #174 , #17, #81

Also provides font hinting support which may allow us to close off #134 but will have to confirm the output to be certain.

• Updates the reference to SixLabors.Fonts bringing with it the new text layout engine.
• Introduces the shared TextOptions type from Fonts which replaces the RendererOptions/TextOptions types that handled text processing options.
• Updates all DrawTextExtensions methods to use the new options type in addition to individual property driven overloads.

[codecov[bot]]

Codecov Report

Merging #177 (7012259) into master (e987bd8) will decrease coverage by 0%. The diff coverage is 82%.

@@          Coverage Diff          @@
##           master   #177   +/-   ##
=====================================
- Coverage      69%    69%   -1%     
=====================================
  Files          89     87    -2     
  Lines        5204   5116   -88     
  Branches     1065   1062    -3     
=====================================
- Hits         3642   3554   -88     
- Misses       1347   1348    +1     
+ Partials      215    214    -1     

Flag	Coverage Δ
unittests	69% <82%> (-1%)	:arrow_down:

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Impacted Files	Coverage Δ
...rc/ImageSharp.Drawing/Processing/DrawingOptions.cs	86% <ø> (-4%)	:arrow_down:
src/ImageSharp.Drawing/Shapes/Text/TextBuilder.cs	0% <0%> (ø)
...rawing/Processing/Extensions/DrawTextExtensions.cs	80% <84%> (-20%)	:arrow_down:
...ing/Processing/DrawingOptionsDefaultsExtensions.cs	100% <100%> (ø)
...p.Drawing/Processing/Extensions/ClearExtensions.cs	100% <100%> (ø)
...ng/Processing/Processors/Text/DrawTextProcessor.cs	88% <100%> (-2%)	:arrow_down:
...ssing/Processors/Text/DrawTextProcessor{TPixel}.cs	96% <100%> (+<1%)	:arrow_up:
src/ImageSharp.Drawing/Processing/ShapeOptions.cs	100% <100%> (ø)

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