Change: [Linkgraph] Allow job threads to be aborted early when clearing schedule (#8416)

When link graph jobs are cleared due to abandoning the game or exiting,
flag the job as aborted.
The link graph job running in a separate thread checks the aborted flag
periodically and terminates processing early if set.
This reduces the delay at game abandon or exit if a long-running job
would otherwise still be running.

src/linkgraph/linkgraphschedule.cpp

@@ -86,6 +86,7 @@ void LinkGraphSchedule::JoinNext()
 /* static */ void LinkGraphSchedule::Run(LinkGraphJob *job)
 {
 	for (uint i = 0; i < lengthof(instance.handlers); ++i) {
+		if (job->IsJobAborted()) return;
 		instance.handlers[i]->Run(*job);
 	}
 
@@ -119,7 +120,7 @@ void LinkGraphSchedule::SpawnAll()
 /* static */ void LinkGraphSchedule::Clear()
 {
 	for (JobList::iterator i(instance.running.begin()); i != instance.running.end(); ++i) {
-		(*i)->JoinThread();
+		(*i)->AbortJob();
 	}
 	instance.running.clear();
 	instance.schedule.clear();