Use unordered_map #2379

Job	Run time
Linux [UBSAN] [lmdb \| clang]	39m 43s
Linux [ASAN] [lmdb \| clang]	37m 57s
Linux [ASAN_INT] [lmdb \| clang] (Errors Ignored)	41m 30s
Linux [TSAN] [lmdb \| clang]	39m 43s
Linux [LEAK] [lmdb \| clang]	40m 49s
Linux [UBSAN] [rocksdb \| clang]	51m 34s
Linux [ASAN] [rocksdb \| clang]	52m 19s
macOS [UBSAN] [lmdb \| clang]	37m 50s
Linux [ASAN_INT] [rocksdb \| clang] (Errors Ignored)	53m 34s
macOS [ASAN] [lmdb \| clang]	30m 20s
Linux [LEAK] [rocksdb \| clang]	54m 37s
macOS [TSAN] [lmdb \| clang]	35m 22s
macOS [UBSAN] [rocksdb \| clang]	48m 28s
macOS [ASAN] [rocksdb \| clang]	46m 0s
macOS [TSAN] [rocksdb \| clang]	55m 56s
	11h 5m 42s

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