Move `is_compiled_string` to public API #7849

Job	Run time
build (windows-2019, Win32, v142, 17, Debug)	1m 36s
build (windows-2019, Win32, v142, 17, Release)	2m 13s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	1m 20s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	1m 55s
build (windows-2019, x64, v141, 14, Debug)	2m 26s
mingw (mingw64)	3m 43s
build (windows-2019, x64, v141, 14, Release)	2m 32s
mingw (ucrt64)	4m 25s
build (windows-2019, x64, v141, 17, Debug)	2m 43s
build (windows-2019, x64, v141, 17, Release)	2m 18s
build (windows-2019, x64, v142, 17, Debug)	1m 37s
build (windows-2019, x64, v142, 17, Release)	2m 26s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	1m 54s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	2m 14s
build (windows-2019, x64, v142, 20, Debug)	1m 42s
build (windows-2019, x64, v142, 20, Release)	3m 26s
build (windows-2022, x64, v143, Debug, 20)	2m 21s
	40m 51s

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