Support for multiframe DNGs

[maruncz]

Hi I implemented support for multiframe DNGs. Teste with penatx PixelShift DNG.

warning: this breaks external API, merging must be coordinated with changes in darktable.

my plan is to change darktable pipeline to support multiple frames, and merge them in demosaic module.

work done:
-refactored RawImage and RawImageData classes to store multiple frames.
-modified internal api
-modified DngDecoder to decode all frames

todo:
-speed optimizations
-cleanup?

possible future:
-modify all decoders to support multiple frames

[maruncz]

Hi i was wondering, is this work so far acceptable into rawspeed?

[codecov]

Codecov Report

Merging #350 (2949e7e) into develop (73742db) will decrease coverage by 0.25%.
The diff coverage is 43.79%.

@@             Coverage Diff             @@
##           develop     #350      +/-   ##
===========================================
- Coverage    57.70%   57.44%   -0.26%     
===========================================
  Files          207      207              
  Lines        11994    12008      +14     
  Branches       288      285       -3     
===========================================
- Hits          6921     6898      -23     
- Misses        4949     4987      +38     
+ Partials       124      123       -1     

Flag	Coverage Δ
integration	47.82% <46.49%> (-0.09%)	⬇️
rpu_u	47.82% <46.49%> (-0.09%)	⬇️
unittests	18.59% <0.42%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
fuzz/librawspeed/decompressors/Cr2Decompressor.cpp	0.00% <0.00%> (ø)
fuzz/librawspeed/decompressors/CrwDecompressor.cpp	0.00% <0.00%> (ø)
...brawspeed/decompressors/DummyLJpegDecompressor.cpp	0.00% <0.00%> (ø)
...uzz/librawspeed/decompressors/FujiDecompressor.cpp	0.00% <0.00%> (ø)
...brawspeed/decompressors/HasselbladDecompressor.cpp	0.00% <0.00%> (ø)
...zz/librawspeed/decompressors/KodakDecompressor.cpp	0.00% <0.00%> (ø)
...zz/librawspeed/decompressors/LJpegDecompressor.cpp	0.00% <0.00%> (ø)
...zz/librawspeed/decompressors/NikonDecompressor.cpp	0.00% <0.00%> (ø)
.../librawspeed/decompressors/OlympusDecompressor.cpp	0.00% <0.00%> (ø)
...rawspeed/decompressors/PanasonicV4Decompressor.cpp	0.00% <0.00%> (ø)
... and 121 more

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