Remove more MSVC 2015 workarounds and fix string_view checks #7681

Job	Run time
build (windows-2019, Win32, v142, 17, Debug)	3m 2s
build (windows-2019, Win32, v142, 17, Release)	3m 8s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	1m 27s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	2m 4s
build (windows-2019, x64, v141, 14, Debug)	2m 11s
mingw (mingw64)	4m 26s
build (windows-2019, x64, v141, 14, Release)	4m 27s
mingw (ucrt64)	5m 13s
build (windows-2019, x64, v141, 17, Debug)	1m 51s
build (windows-2019, x64, v141, 17, Release)	3m 9s
build (windows-2019, x64, v142, 17, Debug)	1m 28s
build (windows-2019, x64, v142, 17, Release)	5m 12s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	4m 38s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	2m 39s
build (windows-2019, x64, v142, 20, Debug)	1m 30s
build (windows-2019, x64, v142, 20, Release)	2m 49s
build (windows-2022, x64, v143, Debug, 20)	2m 23s
	51m 37s

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