add C++20 module #279

Job	Run time
ubuntu cmake	12s
macos cmake	15s
ubuntu (g++, standard)	1m 5s
windows (Win32, standard)	2m 24s
ubuntu (g++, PUGIXML_WCHAR_MODE)	1m 7s
windows (Win32, PUGIXML_WCHAR_MODE)	1m 41s
ubuntu (g++, PUGIXML_COMPACT)	1m 8s
windows (Win32, PUGIXML_COMPACT)	1m 9s
ubuntu (g++, PUGIXML_NO_EXCEPTIONS)	1m 2s
windows (Win32, PUGIXML_NO_EXCEPTIONS)	1m 21s
ubuntu (g++, PUGIXML_STRING_VIEW)	1m 9s
windows (Win32, PUGIXML_STRING_VIEW)	1m 37s
ubuntu (clang++, standard)	49s
windows (x64, standard)	1m 54s
ubuntu (clang++, PUGIXML_WCHAR_MODE)	50s
windows (x64, PUGIXML_WCHAR_MODE)	1m 57s
ubuntu (clang++, PUGIXML_COMPACT)	52s
windows (x64, PUGIXML_COMPACT)	1m 51s
ubuntu (clang++, PUGIXML_NO_EXCEPTIONS)	48s
windows (x64, PUGIXML_NO_EXCEPTIONS)	1m 37s
windows (x64, PUGIXML_STRING_VIEW)	1m 47s
ubuntu (clang++, PUGIXML_STRING_VIEW)	50s
macos (clang++, standard)	55s
macos (clang++, PUGIXML_WCHAR_MODE)	58s
macos (clang++, PUGIXML_COMPACT)	46s
macos (clang++, PUGIXML_NO_EXCEPTIONS)	59s
macos (clang++, PUGIXML_STRING_VIEW)	46s
	31m 49s

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