Draft: Add support for specifying the separator for range types #6742

Job	Run time
build (g++-4.8, Debug, 11)	1m 6s
build (g++-4.8, Release, 11)	1m 6s
build (g++-10, Debug, 11)	58s
build (g++-10, Release, 11)	1m 1s
build (clang++-9, Debug, 11)	48s
build (clang++-9, Release, 11)	1m 7s
build (g++-8, Debug, 14, sudo apt install g++-8)	1m 6s
build (g++-8, Debug, 17, sudo apt install g++-8)	1m 4s
build (g++-9, Debug, 17)	1m 6s
build (g++-10, Debug, 17)	1m 6s
build (g++-11, Debug, 20, sudo apt install g++-11)	1m 5s
build (clang++-8, Debug, 17, -stdlib=libc++, sudo apt install clang-8 libc++-8-dev libc++abi-8-dev)	53s
build (clang++-9, Debug, 17, -DFMT_FUZZ=ON -DFMT_FUZZ_LINKMAIN=ON, sudo apt install clang-9)	53s
build (clang++-11, Debug, 20)	50s
build (clang++-11, Debug, 20, -stdlib=libc++, sudo apt install libc++-11-dev libc++abi-11-dev)	55s
	15m 4s

Provide feedback