Encode reversed images as grayscale or indexed when possible #4402

Job	Run time
unix (ubuntu-22.04, clang++, make)	46s
unix (ubuntu-22.04, g++, cmake)	1m 16s
windows (64, windows-2019)	6m 39s
unix (macos-14, clang++, cmake)	41s
windows (32, windows-2022)	5m 0s
cygwin (32)	7m 56s
windows-mingw-build (64)	1m 10s
macos-static	2m 33s
unix (ubuntu-22.04, clang++, cmake)	54s
freebsd	5m 18s
windows (64, windows-2022)	5m 58s
unix (macos-14, clang++, make)	42s
cygwin (64)	6m 27s
windows (32, windows-2019)	5m 50s
windows-mingw-build (32)	1m 3s
unix (ubuntu-22.04, g++, make)	1m 28s
windows-mingw-testing (windows-2022, 32)	5m 26s
windows-mingw-testing (windows-2022, 64)	5m 8s
windows-mingw-testing (windows-2019, 64)	4m 28s
windows-mingw-testing (windows-2019, 32)	5m 56s
	1h 14m 39s

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