Add a new interface method SecondaryIndex::NewIterator to enable querying the index #3785

Job	Run time
build-linux	16m 54s
build-linux-cmake-with-folly	27m 43s
check-format-and-targets	25s
build-examples	10m 52s
build-linux-clang-13-no_test_run	7m 19s
build-fuzzers	8m 32s
build-linux-clang-no_test_run	11m 54s
build-linux-cmake-mingw	12m 24s
build-linux-cmake-with-benchmark	19m 57s
build-linux-cmake-with-folly-lite-no-test	8m 0s
build-linux-cmake-with-folly-coroutines	32m 18s
build-linux-encrypted_env-no_compression	16m 2s
build-linux-gcc-10-cxx20-no_test_run	9m 48s
build-linux-gcc-11-no_test_run	10m 4s
build-linux-gcc-8-no_test_run	8m 30s
build-linux-make-with-folly	28m 17s
build-linux-make-with-folly-lite-no-test	9m 25s
build-linux-release-rtti	12m 39s
build-linux-release	14m 15s
build-linux-arm	14m 59s
build-linux-clang10-clang-analyze	17m 25s
build-linux-clang10-asan	17m 7s
build-linux-clang10-ubsan	17m 4s
build-linux-clang13-mini-tsan	24m 37s
build-linux-java	15m 17s
build-linux-java-pmd	12m 13s
build-linux-mini-crashtest	29m 59s
build-linux-java-static	11m 41s
build-linux-static_lib-alt_namespace-status_checked	19m 19s
build-linux-unity-and-headers	13m 14s
build-macos	32m 23s
build-macos-cmake (true)	54m 57s
build-macos-cmake (false)	42m 9s
build-macos-java	15m 12s
build-macos-java-static-universal	24m 38s
build-macos-java-static	23m 20s
build-windows-vs2019	52m 50s
	11h 43m 42s

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