Address rare corruption of NFTokenPage linked list (#4945)

* Add fixNFTokenPageLinks amendment:

It was discovered that under rare circumstances the links between
NFTokenPages could be removed.  If this happens, then the
account_objects and account_nfts RPC commands under-report the
NFTokens owned by an account.

The fixNFTokenPageLinks amendment does the following to address
the problem:

- It fixes the underlying problem so no further broken links
  should be created.
- It adds Invariants so, if such damage were introduced in the
  future, an invariant would stop it.
- It adds a new FixLedgerState transaction that repairs
  directories that were damaged in this fashion.
- It adds unit tests for all of it.

src/test/jtx/impl/ledgerStateFix.cpp

@@ -0,0 +1,49 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of rippled: https://github.com/ripple/rippled
+    Copyright (c) 2024 Ripple Labs Inc.
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <test/jtx/ledgerStateFix.h>
+
+#include <xrpld/app/tx/detail/LedgerStateFix.h>
+#include <xrpl/protocol/TxFlags.h>
+#include <xrpl/protocol/jss.h>
+
+namespace ripple {
+namespace test {
+namespace jtx {
+
+namespace ledgerStateFix {
+
+// Fix NFTokenPage links on owner's account.  acct pays fee.
+Json::Value
+nftPageLinks(jtx::Account const& acct, jtx::Account const& owner)
+{
+    Json::Value jv;
+    jv[sfAccount.jsonName] = acct.human();
+    jv[sfLedgerFixType.jsonName] = LedgerStateFix::nfTokenPageLink;
+    jv[sfOwner.jsonName] = owner.human();
+    jv[sfTransactionType.jsonName] = jss::LedgerStateFix;
+    jv[sfFlags.jsonName] = tfUniversal;
+    return jv;
+}
+
+}  // namespace ledgerStateFix
+
+}  // namespace jtx
+}  // namespace test
+}  // namespace ripple