Add DCT/IDCT gbench #14165

Job	Run time
Ubuntu Build release	22m 14s
Ubuntu Build debug	1m 14s
Ubuntu Build asan	1m 43s
Ubuntu Build msan	3m 8s
Ubuntu Build tsan	1m 21s
Ubuntu Build scalar	1m 14s
Ubuntu Build lowprecision	15m 41s
Ubuntu Build coverage	51s
Ubuntu Build release-nojpeg	1m 8s
Ubuntu Build release-lcms2	1m 11s
Ubuntu Build release-system-lcms2	1m 33s
Ubuntu Build release:minimal	1m 35s
Ubuntu Build release:gcc8	1m 14s
Ubuntu Build release:clang-7	1m 32s
MacOS Build release:osx	1m 30s
	57m 9s

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