Restore StyleCop Warnings as Errors

[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 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

Fixes #1658

See SixLabors/SharedInfrastructure#20 for details.

We needed to be more specific with our settings.

[codecov]

Codecov Report

Merging #1664 (1642a67) into master (5966a2e) will not change coverage.
The diff coverage is 95.65%.

@@           Coverage Diff           @@
##           master    #1664   +/-   ##
=======================================
  Coverage   84.32%   84.32%           
=======================================
  Files         816      816           
  Lines       35856    35856           
  Branches     4167     4167           
=======================================
  Hits        30235    30235           
  Misses       4799     4799           
  Partials      822      822           

Flag	Coverage Δ
unittests	84.32% <95.65%> (ø)

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

Impacted Files	Coverage Δ
.../Formats/Tiff/Writers/TiffPaletteWriter{TPixel}.cs	97.10% <0.00%> (ø)
...omponents/Encoder/RgbToYCbCrConverterVectorized.cs	97.97% <100.00%> (ø)
...rp/Formats/Jpeg/Components/FastFloatingPointDCT.cs	100.00% <100.00%> (ø)
src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs	95.16% <100.00%> (ø)

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[antonfirsov]

@JimBobSquarePants wouldn't this result in picking wrong project-level configs in VS for the Debug-InnerLoop solution config?

[JimBobSquarePants]

Configbuilder is odd. Either way seems to do what we want and this is the default generated when you create and copy settings from existing. I hacked it before and VS get complaining something was wrong if I switched between the two.