Add Abgr32 pixel type, extend IPixel<T>

[ynse01]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
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• I have provided test coverage for my change (where applicable)

Description

This adds the Abgr32 Pixel Format, as described in issue #1345.

For most of its implementation, I took inspiration from the Bgra32 pixel format code. It includes the SIMD conversions to other RGB based formats, so conversion performance should be pretty good.

I also fixed, what I think is a bug, in IComponentShuffle. Please check if my understanding of byte shuffling is correct.

I've not added Benchmarks, as there weren't any for Bgra32 also. I expect the performance will be similar to the other RGBA Pixel Formats. Let me know if you want me to add benchmarks.

[brianpopow]

@antonfirsov there seem to be failing tests on macos, which may be related to #1730, could you take a look at this: Failing Tests

[gfoidl]

Can this be sealed?
Sealing would open the door in the JIT to allow de-virtualization, especially with dynamic profile guided optimizaiton (D-PGO).

[codecov]

Codecov Report

Merging #1886 (a94b8c4) into master (ecd3db2) will increase coverage by 0%.
The diff coverage is 96%.

@@           Coverage Diff           @@
##           master   #1886    +/-   ##
=======================================
  Coverage      87%     87%            
=======================================
  Files         957     960     +3     
  Lines       50474   50972   +498     
  Branches     6291    6310    +19     
=======================================
+ Hits        44252   44731   +479     
- Misses       5185    5202    +17     
- Partials     1037    1039     +2     

Flag	Coverage Δ
unittests	87% <96%> (+<1%)	⬆️

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

Impacted Files	Coverage Δ
src/ImageSharp/Color/Color.Conversions.cs	66% <50%> (-3%)	⬇️
...eSharp/PixelFormats/PixelImplementations/Abgr32.cs	86% <86%> (ø)
src/ImageSharp/Common/Helpers/Numerics.cs	97% <100%> (+<1%)	⬆️
...eSharp/Common/Helpers/Shuffle/IComponentShuffle.cs	100% <100%> (ø)
...ImageSharp/PixelFormats/PixelImplementations/A8.cs	90% <100%> (+<1%)	⬆️
...eSharp/PixelFormats/PixelImplementations/Argb32.cs	90% <100%> (+<1%)	⬆️
...geSharp/PixelFormats/PixelImplementations/Bgr24.cs	95% <100%> (+<1%)	⬆️
...eSharp/PixelFormats/PixelImplementations/Bgr565.cs	85% <100%> (+<1%)	⬆️
...eSharp/PixelFormats/PixelImplementations/Bgra32.cs	95% <100%> (+<1%)	⬆️
...harp/PixelFormats/PixelImplementations/Bgra4444.cs	84% <100%> (+<1%)	⬆️
... and 38 more

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[antonfirsov]

LGTM, thanks!

This is a breaking change due to IPixel<T> interface extension.

overlook

[antonfirsov]

Nevermind, all good.