Jpeg decoder refactoring, fixed 1693

[br3aker]

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Description

• SOF/SOS marker parsing code refactoring, added comments
• Fixed Jpeg decoder IndexOutOfRangeException(s) with malformed images #1693, added tests for them
• Huffman tables are now part of the HuffmanScanDecoder

[codecov]

Codecov Report

Merging #1702 (9750014) into master (61b137d) will decrease coverage by 0.03%.
The diff coverage is 94.95%.

@@            Coverage Diff             @@
##           master    #1702      +/-   ##
==========================================
- Coverage   84.33%   84.29%   -0.04%     
==========================================
  Files         816      816              
  Lines       35914    35912       -2     
  Branches     4179     4181       +2     
==========================================
- Hits        30288    30273      -15     
- Misses       4806     4813       +7     
- Partials      820      826       +6     

Flag	Coverage Δ
unittests	84.29% <94.95%> (-0.04%)	⬇️

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

Impacted Files	Coverage Δ
.../Jpeg/Components/Decoder/JpegBlockPostProcessor.cs	100.00% <ø> (ø)
src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs	91.95% <92.18%> (-0.83%)	⬇️
...mats/Jpeg/Components/Decoder/HuffmanScanDecoder.cs	93.54% <95.83%> (-2.55%)	⬇️
...p/Formats/Jpeg/Components/Decoder/JpegComponent.cs	93.87% <100.00%> (-4.13%)	⬇️
...g/Components/Decoder/JpegComponentPostProcessor.cs	92.85% <100.00%> (+0.17%)	⬆️
...Sharp/Formats/Jpeg/Components/Decoder/JpegFrame.cs	100.00% <100.00%> (ø)
...eg/Components/Decoder/SpectralConverter{TPixel}.cs	100.00% <100.00%> (ø)
src/ImageSharp/Formats/Jpeg/JpegThrowHelper.cs	55.55% <0.00%> (-11.12%)	⬇️

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[JimBobSquarePants]

Awesome stuff. Thanks!