filterConserve: Reduce the chances of stack overflow

Observed when running the pos tests after the previous commit, the test
suite didn't say which test caused the stackoverflow, but the stack
trace ended with:

at dotty.tools.dotc.core.Decorators$ListDecorator$.loop$2(Decorators.scala:90)
at dotty.tools.dotc.core.Decorators$ListDecorator$.loop$2(Decorators.scala:90)
at dotty.tools.dotc.core.Decorators$ListDecorator$.filterConserve$extension(Decorators.scala:97)
at dotty.tools.dotc.core.OrderingConstraint.$anonfun$remove$1(OrderingConstraint.scala:453)
at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:237)
at scala.collection.IndexedSeqOptimized.foreach(IndexedSeqOptimized.scala:36)
at scala.collection.IndexedSeqOptimized.foreach$(IndexedSeqOptimized.scala:33)
at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:198)
at scala.collection.TraversableLike.map(TraversableLike.scala:237)
at scala.collection.TraversableLike.map$(TraversableLike.scala:230)
at scala.collection.mutable.ArrayOps$ofRef.map(ArrayOps.scala:198)
at dotty.tools.dotc.core.OrderingConstraint.removeFromBoundss$1(OrderingConstraint.scala:453)
at dotty.tools.dotc.core.OrderingConstraint.$anonfun$remove$4(OrderingConstraint.scala:456)
at dotty.tools.dotc.util.SimpleIdentityMap$MapMore.mapValuesNow(SimpleIdentityMap.scala:209)
at dotty.tools.dotc.core.OrderingConstraint.removeFromOrdering$1(OrderingConstraint.scala:456)
at dotty.tools.dotc.core.OrderingConstraint.remove(OrderingConstraint.scala:458)
at dotty.tools.dotc.core.OrderingConstraint.replace(OrderingConstraint.scala:440)
at dotty.tools.dotc.core.OrderingConstraint.replace(OrderingConstraint.scala:132)
at dotty.tools.dotc.core.Types$TypeVar.instantiateWith(Types.scala:3712)
at dotty.tools.dotc.core.Types$TypeVar.instantiate(Types.scala:3724)
at dotty.tools.dotc.typer.Inferencing.$anonfun$interpolateTypeVars$2(Inferencing.scala:450)
...

Author: smarter

compiler/src/dotty/tools/dotc/core/Decorators.scala

@@ -44,7 +44,7 @@ object Decorators {
     }
   }
 
-  final val MaxFilterRecursions = 1000
+  final val MaxFilterRecursions = 100
 
   /** Implements filterConserve, zipWithConserve methods
    *  on lists that avoid duplication of list nodes where feasible.