On Serenity, SQLServer is started by SystemServer. But on Lagom, it is
manually started by e.g. Ladybird when the application is started, and
killed when the application exits. This means every Ladybird process
starts its own SQLServer, which defeats the purpose of SQLServer acting
as the single process interacting with the database files.
This patch will allow SQLClient to start up a single SQLServer instance,
first checking if one already exists. If it does exist, SQLClient will
simply connect to SQLServer's socket. If it does not exist, SQLClient
will launch SQLServer much like SystemServer would (with a local socket
file, etc.).
The child SQLServer process is double-forked; the grandchild process
becomes the SQLServer process, which the middle child process simply
exits to "detach" the grandchild process from the SQLClient process.
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