Add support for decoding tiff's encoded with LeastSignificantBitFirst

[brianpopow]

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Description

This PR adds support for decoding 1bit tiff's encoded with LeastSignificantBitFirst: pixels are arranged within a byte such that pixels with lower column values are stored in the lower-order bits of the byte.

Also reduce test images size for some images to reduce memory usage and time it takes to execute the tiff tests.

[codecov]

Codecov Report

Merging #1725 (9fbb3f4) into master (51e1870) will decrease coverage by 0.02%.
The diff coverage is 95.45%.

@@            Coverage Diff             @@
##           master    #1725      +/-   ##
==========================================
- Coverage   84.40%   84.38%   -0.03%     
==========================================
  Files         830      830              
  Lines       36262    36288      +26     
  Branches     4238     4241       +3     
==========================================
+ Hits        30607    30621      +14     
- Misses       4839     4850      +11     
- Partials      816      817       +1     

Flag	Coverage Δ
unittests	84.38% <95.45%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
...mageSharp/Formats/Tiff/TiffDecoderOptionsParser.cs	63.63% <33.33%> (-1.25%)	⬇️
...on/Decompressors/ModifiedHuffmanTiffCompression.cs	100.00% <100.00%> (ø)
...mats/Tiff/Compression/Decompressors/T4BitReader.cs	94.30% <100.00%> (+0.09%)	⬆️
...iff/Compression/Decompressors/T4TiffCompression.cs	94.59% <100.00%> (+2.00%)	⬆️
...rmats/Tiff/Compression/TiffDecompressorsFactory.cs	71.42% <100.00%> (ø)
src/ImageSharp/Formats/Tiff/TiffDecoderCore.cs	89.55% <100.00%> (+0.84%)	⬆️
...geSharp/Formats/Tiff/TiffDecoderMetadataCreator.cs	70.37% <0.00%> (-18.52%)	⬇️

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[brianpopow]

I will go ahead and merge this. I want to continue with tiff and I gets more and more complicated to juggle the open PR without creating merge conflicts for myself. Feel still free to comment here on any issue.