Fewer (and more predictable) branches in Range.isEmpty.

Extract branches to be mostly dependent on `isInclusive` and
`step >= 0`. These are often constant, and when they're not
statically constant, they are probably predictable anyway.

This commit upstreams
scala-js/scala-js@a5337ed
from Scala.js.

Author: sjrd

library/src/scala/collection/immutable/Range.scala

@@ -91,10 +91,11 @@ sealed abstract class Range(
   def isInclusive: Boolean
 
   final override val isEmpty: Boolean = (
-    (start > end && step > 0)
-      || (start < end && step < 0)
-      || (start == end && !isInclusive)
-    )
+    if (isInclusive)
+      (if (step >= 0) start > end else start < end)
+    else
+      (if (step >= 0) start >= end else start <= end)
+  )
 
   private[this] val numRangeElements: Int = {
     if (step == 0) throw new IllegalArgumentException("step cannot be 0.")