basic conversion to C++20 #1495

Job	Run time
Linux-GCC9-deps=forcefallback	8m 15s
MSVC-forcefallback-x64	4m 42s
Linux-GCC9-deps=default	1m 21s
Emscripten	2m 54s
MSVC-forcefallback-x86	5m 33s
FreeBSD	3m 56s
Linux-GCC13-deps=forcefallback	8m 41s
MSVC-default-x64	2m 7s
Linux-GCC13-deps=default	1m 46s
MSVC-default-x86	3m 2s
macOS-deps=enabled	1m 51s
MSYS	2m 3s
macOS-deps=disabled	55s
MSYS2-UCRT64-deps=enabled	4m 57s
Linux-Clang11-deps=forcefallback	8m 44s
MSYS2-CLANG64-deps=enabled	3m 20s
clang-cl-forcefallback	6m 13s
Linux-Clang11-deps=default	1m 44s
MSYS2-UCRT64-deps=disabled	3m 24s
clang-cl-default	3m 23s
Linux-Clang19-deps=forcefallback	9m 26s
MSYS2-CLANG64-deps=disabled	2m 31s
Linux-Clang19-deps=default	2m 14s
	1h 33m 2s

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