Internals: Create if statements for triggers during scheduling (#6280) (#6581)

The AstIf nodes conditional on events being triggered used to be created
in V3Clock. Now it is in V3Sched*, in order to avoid having to pass
AstActive in CFunc or MTask bodies. No functional change intended, some
improved optimization due to simplifying timing triggers that were
previously missed, also fixes what seems like a bug in the original
timing commit code.

src/Verilator.cpp

@@ -461,7 +461,7 @@ static void process() {
             V3Sched::schedule(v3Global.rootp());
             V3Sched::transformForks(v3Global.rootp());
 
-            // Convert sense lists into IF statements.
+            // Post scheduling transformations - TODO: this should at least be renamed
             V3Clock::clockAll(v3Global.rootp());
 
             // Cleanup any dly vars or other temps that are simple assignments