Don't use usingTerminal

The usingTerminal method synchronizes the JLine object which can lead to
deadlock if multiple threads call it. When we just to want to read the
attributes of the terminal, but not modify it, there doesn't seem to be
any reason to use a lock.

internal/util-complete/src/main/scala/sbt/internal/util/LineReader.scala

@@ -127,7 +127,7 @@ private[sbt] object JLine {
 
   // When calling this, ensure that enableEcho has been or will be called.
   // TerminalFactory.get will initialize the terminal to disable echo.
-  private def terminal = jline.TerminalFactory.get
+  private[sbt] def terminal = jline.TerminalFactory.get
 
   private def withTerminal[T](f: jline.Terminal => T): T =
     synchronized {

main/src/main/scala/sbt/CommandLineUIService.scala

@@ -27,9 +27,9 @@ trait CommandLineUIService extends InteractionService {
     }
   }
 
-  override def terminalWidth: Int = JLine.usingTerminal(_.getWidth)
+  override def terminalWidth: Int = JLine.terminal.getWidth
 
-  override def terminalHeight: Int = JLine.usingTerminal(_.getHeight)
+  override def terminalHeight: Int = JLine.terminal.getHeight
 }
 
 object CommandLineUIService extends CommandLineUIService

main/src/main/scala/sbt/internal/SettingGraph.scala

@@ -82,7 +82,7 @@ object Graph {
   // [info]   |
   // [info]   +-quux
   def toAscii[A](top: A, children: A => Seq[A], display: A => String, defaultWidth: Int): String = {
-    val maxColumn = math.max(JLine.usingTerminal(_.getWidth), defaultWidth) - 8
+    val maxColumn = math.max(JLine.terminal.getWidth, defaultWidth) - 8
     val twoSpaces = " " + " " // prevent accidentally being converted into a tab
     def limitLine(s: String): String =
       if (s.length > maxColumn) s.slice(0, maxColumn - 2) + ".."

main/src/main/scala/sbt/internal/TaskProgress.scala

@@ -25,7 +25,7 @@ private[sbt] final class TaskProgress
   private[this] val isStopped = new AtomicBoolean(false)
 
   override def initial(): Unit = {
-    ConsoleAppender.setTerminalWidth(JLine.usingTerminal(_.getWidth))
+    ConsoleAppender.setTerminalWidth(JLine.terminal.getWidth)
   }
 
   override def afterReady(task: Task[_]): Unit = {