Eliminate closure in foreachTypeVar

It's fairly hot code, and eliminating the closure also
avoids Int boxing.

Author: odersky

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

@@ -567,11 +567,13 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
 
   def foreachTypeVar(op: TypeVar => Unit): Unit =
     boundsMap.foreachBinding { (poly, entries) =>
-      for (i <- 0 until paramCount(entries))
-        typeVar(entries, i) match {
+      var i = 0
+      val limit = paramCount(entries)
+      while i < limit do
+        typeVar(entries, i) match
           case tv: TypeVar if !tv.inst.exists => op(tv)
           case _ =>
-        }
+        i += 1
     }
 
   private var myUninstVars: mutable.ArrayBuffer[TypeVar] = _