Remove more MSVC 2015 workarounds and fix string_view checks #7680

Job	Run time
build (windows-2019, Win32, v142, 17, Debug)	1m 30s
build (windows-2019, Win32, v142, 17, Release)	2m 13s
mingw (mingw64)	4m 23s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	2m 49s
mingw (ucrt64)	3m 49s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	2m 0s
build (windows-2019, x64, v141, 14, Debug)	1m 38s
build (windows-2019, x64, v141, 14, Release)	1m 49s
build (windows-2019, x64, v141, 17, Debug)	1m 39s
build (windows-2019, x64, v141, 17, Release)	1m 51s
build (windows-2019, x64, v142, 17, Debug)	1m 39s
build (windows-2019, x64, v142, 17, Release)	1m 41s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	1m 47s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	1m 35s
build (windows-2019, x64, v142, 20, Debug)	1m 33s
build (windows-2019, x64, v142, 20, Release)	1m 44s
build (windows-2022, x64, v143, Debug, 20)	2m 24s
	36m 4s

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