Add scaladoc documentation for ReplDriver#redirectOutput

Author: vasilmkd

compiler/src/dotty/tools/repl/ReplDriver.scala

@@ -187,6 +187,17 @@ class ReplDriver(settings: Array[String],
   // TODO: i5069
   final def bind(name: String, value: Any)(using state: State): State = state
 
+  /**
+   * Controls whether the `System.out` and `System.err` streams are set to the provided constructor parameter instance
+   * of [[java.io.PrintStream]] during the execution of the repl. On by default.
+   *
+   * Disabling this can be beneficial when executing a repl instance inside a concurrent environment, for example a
+   * thread pool (such as the Scala compile server in the Scala Plugin for IntelliJ IDEA).
+   *
+   * In such environments, indepently executing `System.setOut` and `System.setErr` without any synchronization can
+   * lead to unpredictable results when restoring the original streams (dependent on the order of execution), leaving
+   * the Java process in an inconsistent state.
+   */
   protected def redirectOutput: Boolean = true
 
   // redirecting the output allows us to test `println` in scripted tests