Add APNG coder support

[dreampiggy]

New Pull Request Checklist

• I have read and understood the CONTRIBUTING guide

• I have read the Documentation

• I have searched for a similar pull request in the project and found none

• I have updated this branch with the latest master to avoid conflicts (via merge from master or rebase)

• I have added the required tests to prove the fix/feature I am adding

• I have updated the documentation (if necessary)

• I have run the tests and they pass

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This merge request fixes / reffers to the following issues: #1060

Pull Request Description

This PR add the build-in support for APNG image format. See here: https://en.wikipedia.org/wiki/APNG

For static PNG image, it can decode the first frame. For APNG image, it can decode the animated image.

This coder conform to SDWebImageProgressiveCoder, which means you can do incremental image loading for APNG frames.

This coder also conform to SDAnimatedImageCoder protocol and can be intergrate in SDAnimatedImageView to support big APNG rendering.

This PR is based on the animated coder refactor branch. So if that branch is merged firstly, the diff may looks more clear. Refactor branch merged

[codecov-io]

Codecov Report

Merging #2149 into 5.x will decrease coverage by 0.93%.
The diff coverage is 49.17%.

@@            Coverage Diff            @@
##              5.x   #2149      +/-   ##
=========================================
- Coverage   74.63%   73.7%   -0.94%     
=========================================
  Files          50      51       +1     
  Lines        6372    6613     +241     
  Branches      575     597      +22     
=========================================
+ Hits         4756    4874     +118     
- Misses       1558    1681     +123     
  Partials       58      58

Impacted Files	Coverage Δ
SDWebImage/SDWebImageCodersManager.m	70.31% <100%> (ø)	⬆️
Tests/Tests/SDWebImageDecoderTests.m	100% <100%> (ø)	⬆️
SDWebImage/SDWebImageAPNGCoder.m	43.26% <43.26%> (ø)
SDWebImage/SDAnimatedImageRep.m	86.53% <82.14%> (-5.13%)	⬇️

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[dreampiggy]

Merged. This is actual a separate component of image decoding and have no conflict with current codebase. I test with iOS & macOS image and it works.

[bpoplauschi]

@dreampiggy is this the same coder from https://github.com/SDWebImage/SDWebImageAPNGCoder? If so, we can do some dependency management to avoid duplicating the code

[dreampiggy]

@bpoplauschi Yes..Nearlly the same for the UIAnimatedImage based animated code. However, current 5.x APNGCoder supports SDWebImageAnimatedCoder for advanced animated image rendering.

You're right, maybe dependency management is better than current subspec management. But however, I think why we need another cocoapods may because that feature (Like WebP coder, or MapKit) need another dependency which is no need for Core Lib.

Since APNG support is done by Apple from Image/IO framework, which is already the main dependency for SDWebImage. It contains the same dependency level as GIF coder. I think separating WebP coder and FLAnimatedImage to another cococapods is more important than APNG or GIF :)

For current that SDWebImageAPNGCoder. Maybe the best way is to close it or mark it as deprecated.

[bpoplauschi]

I see. Basically on the 5.x branch is a more rich version of the APNG coder. OK