Add -Yno-experimental to the library

Author: nicolasstucki

library/src-non-bootstrapped/scala/annotation/internal/experimentalTest.scala

@@ -8,3 +8,5 @@ package internal
  *  It may accidentally be visible while compiling the non-bootstrapped library.
  */
 @experimental def testExperimental = 4
+
+// def test = testExperimental // This should fail if un-commented

project/Build.scala

@@ -1740,7 +1740,10 @@ object Build {
       val base =
         project.withCommonSettings.
           settings(
-            libraryDependencies += "org.scala-lang" % "scala-library" % stdlibVersion
+            libraryDependencies += "org.scala-lang" % "scala-library" % stdlibVersion,
+            // Make sure we do not refer to experimental features outside an experimental scope.
+            // In other words, disable NIGHTLY/SNAPSHOT experimental scope.
+            scalacOptions += "-Yno-experimental",
           ).
           settings(dottyLibrarySettings)
       if (mode == Bootstrapped) {