Fix console task cancellation

When the sbt main loop is blocked by console, any other connected client
is prompted that they can kill the task by typing cancel. The
implementation for the console task is to write some input that will
cause the console to exit because the scala 2.12 console cannot be
safely killed with an interrupt. This input, however, was being blocked
from written to the console because the console input stream was holding
the readThread lock. We can be fix this and propagate the input to the
console we wish to terminate by synchronizing on a different lock
object. This should have no impact outside of cancelling the console
because that is the only place where we call the write method of
WriteableInputStream.

internal/util-logging/src/main/scala/sbt/internal/util/Terminal.scala

@@ -457,7 +457,7 @@ object Terminal {
       extends SimpleInputStream
       with AutoCloseable {
     private[this] val isRaw = new AtomicBoolean(false)
-    final def write(bytes: Int*): Unit = readThread.synchronized {
+    final def write(bytes: Int*): Unit = buffer.synchronized {
       bytes.foreach(b => buffer.put(b))
     }
     def setRawMode(toggle: Boolean): Unit = {
@@ -488,7 +488,7 @@ object Terminal {
       @tailrec def impl(): Unit = {
         val _ = readQueue.take
         val b = in.read
-        buffer.put(b)
+        buffer.synchronized(buffer.put(b))
         if (Thread.interrupted() || (b == -1 && isRaw.get)) closed.set(true)
         else impl()
       }