dotty phase 2: scalafix ExplicitNonNullaryApply (#28949)

* scalafix ExplicitNonNullaryApply prepare

+ Temporarily use com.sandinh:sbt-scalafix because scalacenter/scalafix#1098
+ Add ExplicitNonNullaryApply rule to .scalafix.conf
+ Manually fix a NonNullaryApply case in DeathWatchSpec that cause
  `fixall` fail because ExplicitNonNullaryApply rule incorrectly rewrite
  `context unbecome` to `context unbecome()` instead of `context.unbecome()`

* scalafix ExplicitNonNullaryApply

fix by enabling only ExplicitNonNullaryApply rule in .scalafix.conf then:
```
% sbt -Dakka.build.scalaVersion=2.13.1
> fixall
```

* scalafmtAll

* Revert to ch.epfl.scala:sbt-scalafix

Co-authored-by: Bùi Việt Thành <thanhbv@sandinh.net>

akka-actor-tests/src/test/scala/akka/pattern/PatternSpec.scala

@@ -29,19 +29,19 @@ class PatternSpec extends AkkaSpec {
   "pattern.gracefulStop" must {
 
     "provide Future for stopping an actor" in {
-      val target = system.actorOf(Props[TargetActor])
+      val target = system.actorOf(Props[TargetActor]())
       val result = gracefulStop(target, 5 seconds)
       Await.result(result, 6 seconds) should ===(true)
     }
 
     "complete Future when actor already terminated" in {
-      val target = system.actorOf(Props[TargetActor])
+      val target = system.actorOf(Props[TargetActor]())
       Await.ready(gracefulStop(target, 5 seconds), 6 seconds)
       Await.ready(gracefulStop(target, 1 millis), 1 second)
     }
 
     "complete Future with AskTimeoutException when actor not terminated within timeout" in {
-      val target = system.actorOf(Props[TargetActor])
+      val target = system.actorOf(Props[TargetActor]())
       val latch = TestLatch()
       target ! ((latch, remainingOrDefault))
       intercept[AskTimeoutException] { Await.result(gracefulStop(target, 500 millis), remainingOrDefault) }