IDEA-206386 Stream.toUnmodifiableList autocompletion (and mockJDK-11 to test it)

java/java-tests/testData/codeInsight/completion/normal/ToUnmodifiable.java

@@ -0,0 +1,7 @@
+import java.util.*;
+
+class Foo {
+  void m() {
+    Arrays.asList("a", "b").stream().toUnmod<caret>
+  }
+}