Upgrade to go 1.21, replace golang.org/x/exp/slices with slices #1124

Job	Run time
cpp-lib-build (macos-12, clang, ON)	2m 22s
cpp-lib-build (macos-12, clang, OFF)	3m 56s
build (macos-12, tool)	1m 24s
cpp-lib-build (macos-12, gcc, ON)	2m 44s
build (macos-12, cpp)	14m 59s
cpp-lib-build (macos-12, gcc, OFF)	4m 3s
build (macos-12, csharp)	5m 49s
cpp-lib-build (ubuntu-20.04, clang, ON)	2m 51s
build (macos-12, dart)	4m 52s
cpp-lib-build (ubuntu-20.04, clang, OFF)	3m 49s
cpp-lib-build (ubuntu-20.04, gcc, ON)	2m 29s
build (macos-12, go)	2m 57s
cpp-lib-build (ubuntu-20.04, gcc, OFF)	4m 16s
build (macos-12, java)	1m 36s
cpp-lib-build (windows-2022, clang, ON)	3m 38s
build (macos-12, javascript)	4m 28s
cpp-lib-build (windows-2022, clang, OFF)	4m 34s
cpp-lib-build (windows-2022, cl)	4m 7s
build (macos-12, typescript)	10m 21s
build (macos-12, php)	3m 18s
build (macos-12, python3)	1m 32s
build (ubuntu-20.04, tool)	3m 22s
build (ubuntu-20.04, cpp)	17m 33s
build (ubuntu-20.04, csharp)	5m 25s
build (ubuntu-20.04, dart)	3m 56s
build (ubuntu-20.04, go)	1m 43s
build (ubuntu-20.04, java)	1m 8s
build (ubuntu-20.04, javascript)	1m 49s
build (ubuntu-20.04, typescript)	9m 54s
build (ubuntu-20.04, php)	1m 45s
build (ubuntu-20.04, python3)	1m 13s
build (windows-2022, tool)	1m 30s
build (windows-2022, cpp)	22m 31s
build (windows-2022, csharp)	8m 6s
build (windows-2022, dart)	4m 23s
build (windows-2022, go)	4m 13s
build (windows-2022, java)	4m 16s
build (windows-2022, javascript)	2m 37s
build (windows-2022, typescript)	20m 26s
build (windows-2022, php)	2m 4s
build (windows-2022, python3)	2m 0s
	3h 29m 59s

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