meson: generate trace events for qmp commands

meson: generate trace events for qmp commands

1. Use --gen-trace when generate qmp commands
2. Add corresponding .trace-events files as outputs in qapi_files
   custom target
3. Define global qapi_trace_events list of .trace-events file targets,
   to fill in trace/qapi.build and to use in trace/meson.build
4. In trace/meson.build use the new array as an additional source of
   .trace_events files to be processed

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220126161130.3240892-5-vsementsov@virtuozzo.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>