Add masked_index_benchmark #8081

Job	Run time
build-linux (x86, linux.12xlarge, static, gcc)	17m 28s
build-linux (x86, linux.12xlarge, static, clang)	15m 13s
build-linux (x86, linux.12xlarge, shared, gcc)	17m 20s
build-macos (macos-13, static)	13m 6s
build-macos (macos-13, shared)	12m 36s
build-linux (x86, linux.12xlarge, shared, clang)	15m 2s
build-bazel (x86, linux.12xlarge, gcc)	8m 33s
build-bazel (x86, linux.12xlarge, clang)	7m 45s
build-windows (windows-2022, static)	11m 40s
build-windows (windows-2022, shared)	11m 46s
	2h 10m 29s

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