Make progress lines blink less

The more we call flush, the more likely progress status is to blink. To
reduce the amount of calls to flush, we can instead batch all of the
bytes that are going to be written and wriite them all at once. This
change made progress noticeably less blinky in the zinc project running
the latest sbt snapshot (which frankly was almost siezure inducing when
running publishLocal)

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

@@ -77,12 +77,12 @@ private[sbt] final class ProgressState(
     }
   }
 
-  private[util] def printPrompt(terminal: Terminal, printStream: PrintStream): Unit =
+  private[util] def getPrompt(terminal: Terminal): Array[Byte] = {
     if (terminal.prompt != Prompt.Running && terminal.prompt != Prompt.Batch) {
       val prefix = if (terminal.isAnsiSupported) s"$DeleteLine$CursorLeft1000" else ""
-      printStream.write(prefix.getBytes ++ terminal.prompt.render().getBytes)
-      printStream.flush()
-    }
+      prefix.getBytes ++ terminal.prompt.render().getBytes("UTF-8")
+    } else Array.empty
+  }
   private[util] def write(
       terminal: Terminal,
       bytes: Array[Byte],
@@ -91,15 +91,14 @@ private[sbt] final class ProgressState(
   ): Unit = {
     addBytes(terminal, bytes)
     if (hasProgress) {
+      val toWrite = new ArrayBuffer[Byte]
       terminal.prompt match {
         case a: Prompt.AskUser if a.render.nonEmpty =>
-          printStream.print(DeleteLine + ClearScreenAfterCursor + CursorLeft1000)
-          printStream.flush()
+          toWrite ++= (DeleteLine + ClearScreenAfterCursor + CursorLeft1000).getBytes("UTF-8")
         case _ =>
       }
-      printStream.write(bytes)
-      printStream.write(ClearScreenAfterCursor.getBytes("UTF-8"))
-      printStream.flush()
+      toWrite ++= bytes
+      toWrite ++= ClearScreenAfterCursor.getBytes("UTF-8")
       if (bytes.endsWith(lineSeparatorBytes)) {
         if (progressLines.get.nonEmpty) {
           val lastLine = terminal.prompt match {
@@ -107,10 +106,12 @@ private[sbt] final class ProgressState(
             case _                 => currentLine.getOrElse("")
           }
           val lines = printProgress(terminal, lastLine)
-          printStream.print(ClearScreenAfterCursor + lines)
+          toWrite ++= (ClearScreenAfterCursor + lines).getBytes("UTF-8")
         }
       }
-      printPrompt(terminal, printStream)
+      toWrite ++= getPrompt(terminal)
+      printStream.write(toWrite.toArray)
+      printStream.flush()
     } else printStream.write(bytes)
   }
 
@@ -177,8 +178,9 @@ private[sbt] object ProgressState {
           val lastLine =
             if (isAskUser) terminal.prompt.render() else terminal.getLastLine.getOrElse("")
           state.padding.set(math.max(0, prevSize - currentLength))
-          state.printPrompt(terminal, ps)
-          ps.print(state.printProgress(terminal, lastLine))
+          val toWrite =
+            state.getPrompt(terminal) ++ state.printProgress(terminal, lastLine).getBytes("UTF-8")
+          ps.write(toWrite)
           ps.flush()
         }
       } else if (state.progressLines.get.nonEmpty) {