lwlock: Invert meaning of LW_FLAG_RELEASE_OK

lwlock: Invert meaning of LW_FLAG_RELEASE_OK

Previously, a flag was set to indicate that a lock release should wake up
waiters. Since waking waiters is the default behavior in the majority of
cases, this logic has been inverted. The new LW_FLAG_WAKE_IN_PROGRESS flag is
now set iff wakeups are explicitly inhibited.

The motivation for this change is that in an upcoming commit, content locks
will be implemented independently of lwlocks, with the lock state stored as
part of BufferDesc.state. As all of a buffer's flags are cleared when the
buffer is invalidated, without this change we would have to re-add the
RELEASE_OK flag after clearing the flags; otherwise, the next lock release
would not wake waiters.

It seems good to keep the implementation of lwlocks and buffer content locks
as similar as reasonably possible.

Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/4csodkvvfbfloxxjlkgsnl2lgfv2mtzdl7phqzd4jxjadxm4o5@usw7feyb5bzf