java completion: suggest Objects::nonNull where applicable (IDEA-192789)

java/java-tests/testData/codeInsight/completion/smartType/ObjectsNonNull-out.java

@@ -0,0 +1,12 @@
+import java.util.*;
+
+class MyTest {
+
+  public interface Child {}
+
+  {
+    List<Child> children = new ArrayList<>();
+    children.stream().filter(Objects::nonNull)<caret>
+  }
+
+}

java/java-tests/testData/codeInsight/completion/smartType/ObjectsNonNull.java

@@ -0,0 +1,12 @@
+import java.util.*;
+
+class MyTest {
+
+  public interface Child {}
+
+  {
+    List<Child> children = new ArrayList<>();
+    children.stream().filter(non<caret>)
+  }
+
+}