[libc++] Implement `views::join_with` #8936

Job	Run time
stage1 (frozen-cxx03-headers, clang-20, clang++-20)	7m 21s
stage1 (generic-cxx03, clang-20, clang++-20)	7m 30s
stage1 (generic-cxx26, clang-20, clang++-20)	14m 14s
stage1 (generic-modules, clang-20, clang++-20)	10m 1s
stage1 (generic-gcc, gcc-14, g++-14)	23m 30s
macos (generic-cxx03, macos-15)	14m 47s
windows (clang-cl-dll, false)	3m 27s
macos (generic-cxx23, macos-15)	30m 50s
stage2 (generic-cxx11, clang-20, clang++-20)	8m 58s
windows (clang-cl-static, false)	55m 55s
macos (generic-modules, macos-15)	2m 15s
stage2 (generic-cxx14, clang-20, clang++-20)	9m 4s
windows (clang-cl-no-vcruntime, false)	53m 28s
macos (apple-configuration, macos-15)	39m 47s
stage2 (generic-cxx17, clang-20, clang++-20)	14m 19s
windows (clang-cl-debug, false)	56m 19s
macos (apple-system, macos-13)	4m 0s
stage2 (generic-cxx20, clang-20, clang++-20)	6m 50s
windows (clang-cl-static-crt, false)	2m 56s
macos (apple-system-hardened, macos-13)	1h 1m 22s
stage2 (generic-cxx23, clang-20, clang++-20)	14m 29s
windows (mingw-dll, true)	1h 12m 53s
stage2 (generic-gcc-cxx11, gcc-14, g++-14)	9m 31s
windows (mingw-static, true)	1h 12m 45s
stage2 (generic-cxx23, clang-18, clang++-18)	5m 52s
windows (mingw-dll-i686, true)	3m 27s
stage2 (generic-cxx26, clang-19, clang++-19)	14m 4s
windows (mingw-incomplete-sysroot, true)	7m 11s
stage3	0s
	10h 27m 5s

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