[GR-11702] Logger should log to STDERR, not to STDOUT.

(cherry picked from commit 7991539)

sdk/src/org.graalvm.polyglot/src/org/graalvm/polyglot/Context.java

@@ -973,8 +973,7 @@ public Builder fileSystem(final FileSystem fileSystem) {
          * {@code JavaScriptLanguage} class.<br>
          * <p>
          * If the {@code logHandler} is not set on {@link Engine} nor on {@link Context} the log
-         * messages are printed to {@link #out(java.io.OutputStream) Context's standard output
-         * stream}.
+         * messages are printed to {@link #err(java.io.OutputStream) Context's error output stream}.
          *
          * @param logHandler the {@link Handler} to use for logging in built {@link Context}.
          * @return the {@link Builder}

truffle/src/com.oracle.truffle.api.test/src/com/oracle/truffle/api/test/polyglot/ContextPreInitializationTest.java

@@ -875,18 +875,18 @@ public void testTemporaryEngine() throws Exception {
     public void testLogging() throws Exception {
         setPatchable(FIRST);
         // In context pre-initialization there is no sdk Context to set log handler,
-        // logging is done to System.out
-        final PrintStream origOut = System.out;
-        final ByteArrayOutputStream preInitOut = new ByteArrayOutputStream();
-        try (PrintStream printStream = new PrintStream(preInitOut)) {
-            System.setOut(printStream);
+        // logging is done to System.err
+        final PrintStream origErr = System.err;
+        final ByteArrayOutputStream preInitErr = new ByteArrayOutputStream();
+        try (PrintStream printStream = new PrintStream(preInitErr)) {
+            System.setErr(printStream);
             System.setProperty("polyglot.log.engine.level", "FINE");
             doContextPreinitialize(FIRST);
         } finally {
-            System.setOut(origOut);
+            System.setErr(origErr);
             System.getProperties().remove("polyglot.log.engine.level");
         }
-        final String preInitLog = preInitOut.toString("UTF-8");
+        final String preInitLog = preInitErr.toString("UTF-8");
         assertTrue(preInitLog.contains("Pre-initialized context for language: ContextPreInitializationFirst"));
         List<CountingContext> contexts = new ArrayList<>(emittedContexts);
         assertEquals(1, contexts.size());

truffle/src/com.oracle.truffle.api.test/src/com/oracle/truffle/api/test/polyglot/LoggingTest.java

@@ -441,12 +441,12 @@ public boolean test(final LoggingContext context, final Collection<TruffleLogger
                 return false;
             }
         };
-        final ByteArrayOutputStream out = new ByteArrayOutputStream();
-        try (Context ctx = Context.newBuilder().out(out).build()) {
+        final ByteArrayOutputStream err = new ByteArrayOutputStream();
+        try (Context ctx = Context.newBuilder().err(err).build()) {
             ctx.eval(LoggingLanguageFirst.ID, "");
         }
-        out.close();
-        final String output = new String(out.toByteArray());
+        err.close();
+        final String output = new String(err.toByteArray());
         final Pattern p = Pattern.compile("\\[(.*)\\]\\sWARNING:\\s(.*)");
         for (String line : output.split("\n")) {
             final Matcher m = p.matcher(line);

truffle/src/com.oracle.truffle.polyglot/src/com/oracle/truffle/polyglot/PolyglotEngineImpl.java

@@ -1015,7 +1015,7 @@ public synchronized Context createContext(OutputStream configOut, OutputStream c
         }
 
         Handler useHandler = logHandler != null ? logHandler : this.logHandler;
-        useHandler = useHandler != null ? useHandler : PolyglotLogHandler.createStreamHandler(useOut, false, true);
+        useHandler = useHandler != null ? useHandler : PolyglotLogHandler.createStreamHandler(useErr, false, true);
 
         final InputStream useIn = configIn == null ? this.in : configIn;
 

truffle/src/com.oracle.truffle.polyglot/src/com/oracle/truffle/polyglot/PolyglotImpl.java

@@ -191,7 +191,7 @@ public Engine buildEngine(OutputStream out, OutputStream err, InputStream in, Ma
      */
     @Override
     public void preInitializeEngine() {
-        final Handler logHandler = PolyglotLogHandler.createStreamHandler(System.out, false, true);
+        final Handler logHandler = PolyglotLogHandler.createStreamHandler(System.err, false, true);
         try {
             final PolyglotEngineImpl preInitializedEngine = PolyglotEngineImpl.preInitialize(
                             this,