Add C++20 module interface file and tests #671

Job	Run time
build (windows-latest, x86, Debug, 11)	4m 1s
build (windows-latest, x86, Debug, 14)	3m 32s
build (windows-latest, x86, Debug, 17)	3m 25s
build (windows-latest, x86, Debug, 20)	3m 46s
build (windows-latest, x86, Release, 11)	5m 50s
build (windows-latest, x86, Release, 14)	5m 19s
build (windows-latest, x86, Release, 17)	3m 19s
build (windows-latest, x86, Release, 20)	4m 1s
build (windows-latest, x64, Debug, 11)	5m 43s
build (windows-latest, x64, Debug, 14)	4m 38s
build (windows-latest, x64, Debug, 17)	3m 34s
build (windows-latest, x64, Debug, 20)	4m 3s
build (windows-latest, x64, Release, 11)	3m 23s
build (windows-latest, x64, Release, 14)	3m 37s
build (windows-latest, x64, Release, 17)	3m 25s
build (windows-latest, x64, Release, 20)	3m 29s
build (windows-2019, x86, Debug, 11)	3m 27s
build (windows-2019, x86, Debug, 14)	3m 19s
build (windows-2019, x86, Debug, 17)	3m 15s
build (windows-2019, x86, Debug, 20)	3m 25s
build (windows-2019, x86, Release, 11)	3m 21s
build (windows-2019, x86, Release, 14)	3m 22s
build (windows-2019, x86, Release, 17)	3m 49s
build (windows-2019, x86, Release, 20)	3m 10s
build (windows-2019, x64, Debug, 11)	3m 8s
build (windows-2019, x64, Debug, 14)	3m 49s
build (windows-2019, x64, Debug, 17)	3m 21s
build (windows-2019, x64, Debug, 20)	3m 23s
build (windows-2019, x64, Release, 11)	3m 21s
build (windows-2019, x64, Release, 14)	3m 26s
build (windows-2019, x64, Release, 17)	3m 18s
build (windows-2019, x64, Release, 20)	3m 57s
	1h 59m 56s

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