+build Add sort imports support. (#28780)

* Add scalafix plugin for jdk 9.
* Add command alias sortImports.
* Excludes some sources from SortImports.
* Update SortImports to 0.4.0
* Sort imports with `sortImports` command.

akka-stream/src/main/scala/akka/stream/impl/Throttle.scala

@@ -4,15 +4,15 @@
 
 package akka.stream.impl
 
+import scala.concurrent.duration.{ FiniteDuration, _ }
+
 import akka.annotation.InternalApi
+import akka.stream._
 import akka.stream.ThrottleMode.{ Enforcing, Shaping }
 import akka.stream.impl.fusing.GraphStages.SimpleLinearGraphStage
 import akka.stream.stage._
-import akka.stream._
 import akka.util.NanoTimeTokenBucket
 
-import scala.concurrent.duration.{ FiniteDuration, _ }
-
 /**
  * INTERNAL API
  */