add util to modify repl tests

Author: bjornregnell

repl-test-update/README.md

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+# Small fix to update all repl test-resources
+
+Made to fix this issue:
+https://github.com/lampepfl/dotty/issues/12981 

repl-test-update/build.sbt

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+scalaVersion := "3.0.0"

repl-test-update/project/build.properties

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+sbt.version=1.5.4

repl-test-update/run-insert-error.scala

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+def replTestDir = "../compiler/test-resources/repl"
+
+def list(dir: String = "."): Vector[String] =
+    Option(new java.io.File(dir).list).map(_.toVector).getOrElse(Vector())
+
+def loadLines(fileName: String, enc: String = "UTF-8"): Vector[String] = 
+  var result = Vector.empty[String]
+  val source = scala.io.Source.fromFile(fileName, enc)
+  try result = source.getLines().toVector finally source.close()
+  result
+
+def saveString(text: String, fileName: String, enc: String = "UTF-8"): Unit = 
+  val f = new java.io.File(fileName)
+  val pw = new java.io.PrintWriter(f, enc)
+  try pw.write(text) finally pw.close()
+
+
+@main 
+def run_insert_error(): Unit = 
+  for f <- list(replTestDir) do
+    val fileName = s"$replTestDir/$f"
+    print(s"\nprocessing: $fileName")
+    val lines = loadLines(fileName)
+    var result = Vector[String]() 
+    for i <- lines.indices do
+      result :+= lines(i)
+      if lines(i).startsWith("scala>") && 
+         lines.lift(i + 1).map(_.startsWith("1 | ")).getOrElse(false) 
+      then
+        result :+= "-- Error:"
+
+    val msg = 
+     if lines == result then Console.GREEN + " unmodified" + Console.RESET
+     else Console.RED + " *** MODIFIED" + Console.RESET
+    println(msg)
+    if lines != result then 
+      println("\nbefore ==========>\n" + lines.mkString("\n"))
+      println("\nafter  ==========>\n" + result.mkString("\n"))
+      saveString(result.mkString("\n"), fileName)