The existing code properly parses the network_id parameter from the
the configuration file, but it does not properly set up the code to
use the value correctly. As a result the configured `network_id` is
ignored.

ThreadSafetyAnalysis was used to identify race conditions in this file.
This analysis was modivated by a (rare) crash while running unit tests.

Add locks to Shard flagged by ThreadSafetyAnalysis

While there should never be a missing node when copying the SHAMap,
rippled should not terminate when there's an error rotating the
database. This patch aborts the database rotation rather than aborting rippled.

A few unit tests have historically generated a lot of noise
to the console from log writes.  This noise was not useful
and made it harder to locate actual test failures.

By changing the log level of these tests from
- severities::kError to
- severities::kDisabled
it was possible to remove that noise coming from the logs.

The existing code would, incorrectly, allow negative amounts in offers
for non-fungible tokens. Such offers would be handled very differently
depending on the context: a direct offer would fail with an error code
indicating an internal processing error, whereas brokered offers would
improperly succeed.

This commit introduces the `fixNFTokenNegOffer` amendment that detects
such offers during creation and returns an appropriate error code.

The commit also extends the existing code to allow for buy offers that
contain a `Destination` field, so that a specific broker can be set in
the offer.

An incorrect SQL query could cause the server to improperly
configure its voting state after a restart; typically, this
would manifest as an apparent failure to store a vote which
the administrator of the server had configured.

This commit fixes the broken SQL and ensures that amendment
votes are properly reloaded post-restart and closes #4220.

The peer discovery protocol depends on peers exchanging messages
listing IP addresses for other peers.

Under normal circumstances, these messages should not be sent
frequently; the existing code would track the earliest time a
new message should be processed, but did not actually enforce
that limit.

The XLS-20 implementation contained two bugs that would require the
introduction of amendments. This complicates the adoption of XLS-20
by requiring a staggered amendment activation, first of the two fix
amendments, followed by the `NonFungibleTokensV1` amendment.

After consideration, the consensus among node operators is that the
process should be simplified by the introduction of a new amendment
that, if enabled, would behaves as if the `NonFungibleTokensV1` and
the two fix amendments (`fixNFTokenDirV1` and `fixNFTokenNegOffer`)
were activated at once.

This commit implements this proposal; it does not introduce any new
functionality or additional features, above and beyond that offered
by the existing amendments.

The existing spinlock code, used to protect SHAMapInnerNode
child lists, has a mistake that can allow the same child to
be repeatedly locked under some circumstances.

The bug was in the `SpinBitLock::lock` loop condition check
and would result in the loop terminating early.

This commit fixes this and further simplifies the lock loop
making the correctness of the code easier to verify without
sacrificing performance.

It also promotes the spinlock class from an implementation
detail to a more general purpose, easier to use lock class
with clearer semantics. Two different lock types now allow
developers to easily grab either a single spinlock from an
a group of spinlocks (packed in an unsigned integer) or to
grab all of the spinlocks at once.

While this commit makes spinlocks more widely available to
developers, they are rarely the best tool for the job. Use
them judiciously and only after careful consideration.