MCOL-4912 This patch introduces Extent Map index to improve EM scaleability

EM scaleability project has two parts: phase1 and phase2.
        This is phase1 that brings EM index to speed up(from O(n) down
        to the speed of boost::unordered_map) EM lookups looking for
        <dbroot, oid, partition> tuple to turn it into LBID,
        e.g. most bulk insertion meta info operations.
        The basis is boost::shared_managed_object where EMIndex is
        stored. Whilst it is not debug-friendly it allows to put a
        nested structs into shmem. EMIndex has 3 tiers. Top down description:
        vector of dbroots, map of oids to partition vectors, partition
        vectors that have EM indices.
        Separate EM methods now queries index before they do EM run.
        EMIndex has a separate shmem file with the fixed id
        MCS-shm-00060001.

utils/rwlock/rwlock.h

@@ -1,4 +1,5 @@
 /* Copyright (C) 2014 InfiniDB, Inc.
+   Copyright (C) 2016-2022 MariaDB Corporation
 
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License
@@ -26,6 +27,8 @@
 
 #pragma once
 
+#include <array>
+
 #include <unistd.h>
 #include <stdexcept>
 
@@ -42,6 +45,10 @@
 
 namespace rwlock
 {
+const std::array<const std::string, 7> RWLockNames = {
+    "all", "VSS", "ExtentMap", "FreeList", "VBBM", "CopyLocks", "ExtentMapIndex",
+};
+
 /// the layout of the shmseg
 struct State
 {