BAEL-3938: Add new section on Java 10 Collectors.toUnmodifiableList() (#10488)

* Add java10 examples in the style of the existing examples

The existing examples in core-java-streams-2 module still had system out in them instead of assertions, so I kept that style to keep the article consistent.

* Remove code example that is not in the article

core-java-modules/core-java-10/src/test/java/com/baeldung/java10/streams/StreamToImmutableJava10UnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.java10.streams;
+
+import static java.util.stream.Collectors.toUnmodifiableList;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.Test;
+
+public class StreamToImmutableJava10UnitTest {
+
+    @Test
+    public void whenUsingCollectorsToUnmodifiableList_thenSuccess() {
+        List<String> givenList = Arrays.asList("a", "b", "c");
+        List<String> result = givenList.stream()
+            .collect(toUnmodifiableList());
+
+        System.out.println(result.getClass());
+    }
+}