Add test case on unused with Splitter transform

Currently UnusedParams must be before Splitter. This limitation in only on the current implementation.

Author: nicolasstucki

tests/run/unused-27.check

@@ -0,0 +1,3 @@
+block
+x
+foo

tests/run/unused-27.scala

@@ -0,0 +1,15 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    ({
+      println("block")
+      foo
+    })(x)
+  }
+  def foo(unused a: Int): Unit = {
+    println("foo")
+  }
+  def x: Int = {
+    println("x")
+    42
+  }
+}

tests/run/unused-28.check

@@ -0,0 +1,4 @@
+x
+foo
+x
+bar

tests/run/unused-28.scala

@@ -0,0 +1,18 @@
+object Test {
+  var a = true
+  def main(args: Array[String]): Unit = {
+    (if (a) foo else bar)(x)
+    a = false
+    (if (a) foo else bar)(x)
+  }
+  def foo(unused a: Int): Unit = {
+    println("foo")
+  }
+  def bar(unused a: Int): Unit = {
+    println("bar")
+  }
+  def x: Int = {
+    println("x")
+    42
+  }
+}