Remove more MSVC 2015 workarounds and fix string_view checks #7682

Job	Run time
build (windows-2019, Win32, v142, 17, Debug)	1m 21s
build (windows-2019, Win32, v142, 17, Release)	3m 1s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	1m 54s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	3m 14s
build (windows-2019, x64, v141, 14, Debug)	1m 45s
build (windows-2019, x64, v141, 14, Release)	2m 20s
build (windows-2019, x64, v141, 17, Debug)	1m 47s
build (windows-2019, x64, v141, 17, Release)	2m 10s
build (windows-2019, x64, v142, 17, Debug)	1m 9s
build (windows-2019, x64, v142, 17, Release)	2m 29s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	2m 12s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	1m 59s
build (windows-2019, x64, v142, 20, Debug)	1m 30s
build (windows-2019, x64, v142, 20, Release)	2m 47s
mingw (mingw64)	4m 1s
build (windows-2022, x64, v143, Debug, 20)	2m 17s
mingw (ucrt64)	3m 49s
	39m 45s

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